def call_ss_again(stack_group, previous_frame, extras=None):
wait_each_step = len(stack_group) < 3
runtime = 1.0 if len(stack_group) < 2 else 0.5 if len(
stack_group) < 6 else 0.20
extra_anims = []
if len(stack_group) > 2:
extra_anims.append(
ApplyMethod(
stack_group.shift,
DOWN * previous_frame.get_height() +
DOWN * SMALL_BUFF))
if extras:
extra_anims.extend(extras)
f = StackFrame(ss_bad_code,
'StrangeSqrt(0)',
1, ['a', 'b'],
width=frame_width)
f.next_to(previous_frame, UP, buff=SMALL_BUFF)
self.play(*extra_anims,
ss_bad_code.highlight_lines,
1,
f.set_line,
1,
FadeIn(f),
MaintainPositionRelativeTo(f, previous_frame),
run_time=runtime)
if wait_each_step:
self.wait()
self.play(ss_bad_code.highlight_lines,
2,
f.set_line,
2,
f.update_slot,
'a',
0,
run_time=runtime)
if wait_each_step:
self.wait()
self.play(ss_bad_code.highlight_lines,
3,
f.set_line,
3,
run_time=runtime)
if wait_each_step:
self.wait()
stack_group.add(f)
return f
def construct(self):
frame_width = 3
f1 = StackFrame('foo()', 1, ['a', 'b', ('c', 2)], width=frame_width)
self.play(FadeIn(f1))
self.play(f1.set_line, 2)
self.play(f1.set_line, 3)
self.play(f1.update_slot, 'b', 42)
self.play(f1.set_line, 4, f1.update_slot, 'a', 43)
f2 = StackFrame('bar(1, 2, 3)', 1, ['x'], width=frame_width)
f2.next_to(f1, DOWN, buff=SMALL_BUFF)
self.play(FadeIn(f2))
self.wait()
self.play(FadeOut(f1), FadeOut(f2))
self.wait()
def construct(self):
code_scale = 0.75
ss_code = CodeBlock(
'Java',
r"""
public static double StrangeSqrt(double a) {
if (a < 0) {
double b = StrangeSqrt(a * -1);
return b;
}
return Math.sqrt(a);
}
""",
code_scale=code_scale,
)
t1 = TextMobject(
'Consider this somewhat strange square root function:')
t1.next_to(ss_code, UP, buff=LARGE_BUFF)
self.play(
FadeIn(t1),
ShowCreation(ss_code),
)
self.wait(duration=2.5)
t2 = TextMobject(
'It has a recursive call, meaning \\textit{it calls itself.}')
t2.next_to(ss_code, DOWN, buff=LARGE_BUFF)
# 012345 6 7 8901234567890 1 2345
# double b = StrangeSqrt(a * -1);
rl = ss_code.get_code().get_lines(3)
rc_highlight = SurroundingRectangle(rl[8:-1])
self.play(
FadeIn(t2),
FadeIn(rc_highlight),
)
self.wait(duration=3)
self.play(
FadeOut(t2),
FadeOut(rc_highlight),
)
# Run with a positive input
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
double n = StrangeSqrt(4);
}
""",
line_offset=7,
code_scale=code_scale - 0.1,
)
frame_width = 3.5
main_frame = StackFrame(main_code,
'main()',
9, ['n'],
width=frame_width)
main_code.highlight_lines(9)
VGroup(main_code, main_frame).arrange(RIGHT,
buff=LARGE_BUFF).to_edge(DOWN)
t3 = TextMobject("Let's see what it does with a positive input...")\
.next_to(ss_code, DOWN, buff=LARGE_BUFF)
self.play(
FadeOut(t1),
MaintainPositionRelativeTo(t1, ss_code),
ss_code.to_edge,
UP,
FadeIn(t3),
MaintainPositionRelativeTo(t3, ss_code),
)
self.wait()
self.play(
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
self.wait()
ss_frame = StackFrame(ss_code,
'StrangeSqrt(4)',
1, ['a', 'b'],
width=frame_width)
ss_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
xi = main_code.pre_call(ss_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(ss_frame, UP),
FadeOut(t3),
)
ss_code.post_control_transfer(xi, self)
self.wait()
self.play(
ss_code.highlight_lines,
2,
ss_frame.set_line,
2,
ss_frame.update_slot,
'a',
4,
)
self.wait()
self.play(
ss_code.highlight_lines,
6,
ss_frame.set_line,
6,
)
self.wait()
xi = ss_code.pre_return(main_code, 9)
self.play(
*ss_code.get_control_transfer_clockwise(xi),
Uncreate(ss_frame),
)
main_code.post_control_transfer(xi, self)
self.wait()
t1 = TextMobject('That seems pretty normal...').next_to(
ss_code, DOWN, buff=LARGE_BUFF)
self.play(
main_code.highlight_lines,
10,
main_frame.set_line,
10,
main_frame.update_slot,
'n',
2,
FadeIn(t1),
)
self.wait(duration=2)
t2 = TextMobject("Let's try it with a negative input...")\
.next_to(ss_code, DOWN, buff=LARGE_BUFF)
self.play(
FadeOutAndShiftDown(main_code),
FadeOutAndShiftDown(main_frame),
FadeOut(t1),
FadeIn(t2),
)
# Run with a negative input and see the recursion
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
double n = StrangeSqrt(-4);
}
""",
line_offset=7,
code_scale=code_scale - 0.1,
)
main_frame = StackFrame(main_code,
'main()',
9, ['n'],
width=frame_width)
main_code.highlight_lines(9)
VGroup(main_code, main_frame).arrange(RIGHT,
buff=LARGE_BUFF).to_edge(DOWN)
self.play(
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
self.wait()
ss_frame = StackFrame(ss_code,
'StrangeSqrt(-4)',
1, ['a', 'b'],
width=frame_width)
ss_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
xi = main_code.pre_call(ss_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(ss_frame, UP),
FadeOut(t2),
)
ss_code.post_control_transfer(xi, self)
self.wait()
self.play(
ss_code.highlight_lines,
2,
ss_frame.set_line,
2,
ss_frame.update_slot,
'a',
-4,
)
self.wait()
self.play(
ss_code.highlight_lines,
3,
ss_frame.set_line,
3,
)
self.wait()
self.play(Indicate(rl[8:-1]), )
ss2_frame = StackFrame(ss_code,
'StrangeSqrt(4)',
1, ['a', 'b'],
width=frame_width)
ss2_frame.next_to(ss_frame, UP, buff=SMALL_BUFF)
r1_call_site_rect = ss_code.get_current_highlight().copy().set_color(
WHITE)
self.play(
FadeInFrom(ss2_frame, UP),
ss_code.highlight_lines,
1,
FadeIn(r1_call_site_rect),
)
self.wait()
stack = VGroup(main_frame, ss_frame, ss2_frame)
t1 = TextMobject('Same function, but with\\\\a new frame on the stack')\
.next_to(stack, LEFT, buff=LARGE_BUFF).shift(UP * 0.5)
a = Arrow(t1.get_right(), ss2_frame.get_left(), stroke_width=3)
self.play(
FadeIn(t1),
GrowArrow(a),
)
self.wait(duration=2)
# Now we have a positive input again
self.play(
ss_code.highlight_lines,
2,
ss2_frame.set_line,
2,
ss2_frame.update_slot,
'a',
4,
)
self.wait()
self.play(
ss_code.highlight_lines,
6,
ss2_frame.set_line,
6,
FadeOut(t1),
FadeOut(a),
)
self.wait()
t1 = TextMobject('The stack tells us where to return,\\\\and with which values')\
.next_to(stack, LEFT, buff=LARGE_BUFF).shift(UP * 0.5)
a = Arrow(t1.get_right(), ss_frame.get_left(), stroke_width=3)
self.play(
FadeIn(t1),
GrowArrow(a),
)
self.wait(duration=2)
# Return back to line 3...
self.play(
FadeOut(r1_call_site_rect),
Uncreate(ss2_frame),
ss_code.highlight_lines,
3,
ss_frame.set_line,
3,
)
self.wait()
self.play(
ss_code.highlight_lines,
4,
ss_frame.set_line,
4,
ss_frame.update_slot,
'b',
2,
FadeOut(t1),
FadeOut(a),
)
self.wait()
xi = ss_code.pre_return(main_code, 9)
self.play(
*ss_code.get_control_transfer_clockwise(xi),
Uncreate(ss_frame),
)
main_code.post_control_transfer(xi, self)
self.wait()
self.play(
main_code.highlight_lines,
10,
main_frame.set_line,
10,
main_frame.update_slot,
'n',
2,
)
self.wait()
t1 = TextMobject(
'Thinking about the call stack can help you keep track of\\\\'
'what a recursive function is doing at any given moment.').next_to(
ss_code, DOWN, buff=LARGE_BUFF)
self.play(
FadeOutAndShiftDown(main_code),
FadeOutAndShiftDown(main_frame),
FadeIn(t1),
)
self.wait(duration=3)
t2 = TextMobject('Try writing down part of the stack as you go.')\
.next_to(t2, DOWN, buff=LARGE_BUFF)
self.play(FadeInFromDown(t2))
self.wait(duration=2)
self.play(
FadeOut(t1),
FadeOut(t2),
)
self.wait()
def construct(self):
# - Now, let's change this a bit and break it!
# - Now modify it (a <= 0) and call it with foo(0).
# - switch it out for the broken one, and highlight and note the change.
code_scale = 0.75
ss_good_code = CodeBlock(
'Java',
r"""
public static double StrangeSqrt(double a) {
if (a < 0) {
double b = StrangeSqrt(a * -1);
return b;
}
return Math.sqrt(a);
}
""",
code_scale=code_scale,
)
ss_good_code.to_edge(UP)
self.add(ss_good_code)
t1 = TextMobject(
"Let's break this code in a very small way and\\\\see what happens..."
)
t1.next_to(ss_good_code, DOWN, buff=LARGE_BUFF)
self.play(FadeIn(t1))
self.wait()
gl2 = ss_good_code.get_code().get_lines(2)
ghr = SurroundingRectangle(gl2[3:6])
self.play(ShowCreation(ghr))
self.wait()
ss_bad_code = CodeBlock(
'Java',
r"""
public static double StrangeSqrt(double a) {
if (a <= 0) {
double b = StrangeSqrt(a * -1);
return b;
}
return Math.sqrt(a);
}
""",
code_scale=code_scale,
)
ss_bad_code.to_edge(UP)
bl2 = ss_bad_code.get_code().get_lines(2)
bhr = SurroundingRectangle(bl2[3:7])
self.play(
ReplacementTransform(ss_good_code, ss_bad_code),
ReplacementTransform(ghr, bhr),
)
self.wait()
t2 = TextMobject(
"This small change will have a big effect on one case: 0\\\\"
"Let's run it and see.").next_to(ss_bad_code,
DOWN,
buff=LARGE_BUFF)
self.play(
FadeOut(t1),
FadeIn(t2),
)
self.wait(duration=3)
self.play(
FadeOut(t2),
FadeOut(bhr),
)
self.wait()
# - Start stepping through this and see the stack start to grow forever.
main_code = CodeBlock(
'Java',
r"""
public static void main(String[] args) {
double n = StrangeSqrt(0);
}
""",
line_offset=7,
code_scale=code_scale - 0.1,
)
frame_width = 3.5
main_frame = StackFrame(main_code,
'main()',
9, ['n'],
width=frame_width)
main_code.highlight_lines(9)
VGroup(main_code, main_frame).arrange(RIGHT,
buff=LARGE_BUFF).to_edge(DOWN)
self.play(
FadeInFromDown(main_frame),
FadeInFromDown(main_code),
)
self.wait()
ss_frame = StackFrame(ss_bad_code,
'StrangeSqrt(0)',
1, ['a', 'b'],
width=frame_width)
ss_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
xi = main_code.pre_call(ss_bad_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(ss_frame, UP),
)
ss_bad_code.post_control_transfer(xi, self)
self.wait()
self.play(ss_bad_code.highlight_lines, 2, ss_frame.set_line, 2,
ss_frame.update_slot, 'a', 0)
self.wait()
self.play(ss_bad_code.highlight_lines, 3, ss_frame.set_line, 3)
self.wait()
def call_ss_again(stack_group, previous_frame, extras=None):
wait_each_step = len(stack_group) < 3
runtime = 1.0 if len(stack_group) < 2 else 0.5 if len(
stack_group) < 6 else 0.20
extra_anims = []
if len(stack_group) > 2:
extra_anims.append(
ApplyMethod(
stack_group.shift,
DOWN * previous_frame.get_height() +
DOWN * SMALL_BUFF))
if extras:
extra_anims.extend(extras)
f = StackFrame(ss_bad_code,
'StrangeSqrt(0)',
1, ['a', 'b'],
width=frame_width)
f.next_to(previous_frame, UP, buff=SMALL_BUFF)
self.play(*extra_anims,
ss_bad_code.highlight_lines,
1,
f.set_line,
1,
FadeIn(f),
MaintainPositionRelativeTo(f, previous_frame),
run_time=runtime)
if wait_each_step:
self.wait()
self.play(ss_bad_code.highlight_lines,
2,
f.set_line,
2,
f.update_slot,
'a',
0,
run_time=runtime)
if wait_each_step:
self.wait()
self.play(ss_bad_code.highlight_lines,
3,
f.set_line,
3,
run_time=runtime)
if wait_each_step:
self.wait()
stack_group.add(f)
return f
sg = VGroup(main_frame, ss_frame)
curr_ss_frame = ss_frame
for i in range(3):
curr_ss_frame = call_ss_again(sg, curr_ss_frame)
# - When will this program end? Never?
t1 = TextMobject("Hrm... when is this going to end??").next_to(
main_code, UP, buff=LARGE_BUFF)
extra_text = [FadeIn(t1)]
for i in range(4):
curr_ss_frame = call_ss_again(sg, curr_ss_frame, extra_text)
extra_text = None
t2 = TextMobject("Never?").next_to(main_code, UP, buff=LARGE_BUFF)
extra_text = [FadeOut(t1), FadeIn(t2)]
for i in range(4):
curr_ss_frame = call_ss_again(sg, curr_ss_frame, extra_text)
extra_text = None
sg.save_state()
t3 = TextMobject("The stack is getting quite deep!").next_to(
main_code, UP, buff=LARGE_BUFF)
self.play(sg.scale, 0.20, {'about_edge': TOP}, FadeOut(t2), FadeIn(t3))
self.wait(duration=2)
self.play(sg.restore)
extra_text = [FadeOut(t3)]
for i in range(4):
curr_ss_frame = call_ss_again(sg, curr_ss_frame, extra_text)
extra_text = None
# - Well, the stack is finite, so eventually you get a SO.
# Use the Java SO exception and show it hit and stop.
so_frame = StackFrame(ss_bad_code,
'StrangeSqrt(0)',
1, ['a', 'b'],
width=frame_width)
so_frame.slots().set_color(ORANGE)
so_frame.header_line().set_color(ORANGE)
so_frame.background_rect().set_fill(color=[BLACK, RED])
so_frame.next_to(curr_ss_frame, UP, buff=SMALL_BUFF)
so_exception = TextMobject(
'\\texttt{Exception in thread "main"\\\\java.lang.StackOverflowError}',
).set_color(YELLOW).scale(0.75).next_to(main_code, UP, buff=LARGE_BUFF)
self.play(sg.shift,
DOWN * so_frame.get_height() + DOWN * SMALL_BUFF,
ss_bad_code.get_current_highlight().set_color, ORANGE,
FadeIn(so_frame),
MaintainPositionRelativeTo(so_frame, curr_ss_frame),
Write(so_exception))
sg.add(so_frame)
self.wait(duration=2)
ss_bad_code.generate_target()
so_exception.generate_target()
ss_bad_code.target.scale(0.75)
g = VGroup(so_exception.target,
ss_bad_code.target).arrange(RIGHT, buff=LARGE_BUFF)
g.to_edge(UP)
sg.generate_target()
sg.target.scale(0.15).next_to(g, DOWN).to_edge(RIGHT)
t1 = TextMobject(
"Space for the call stack is limited,\\\\so we can't make recursive calls forever!"
)
self.play(
*[MoveToTarget(t) for t in [so_exception, ss_bad_code, sg]],
FadeOutAndShiftDown(main_code),
FadeInFromDown(t1),
)
self.wait(duration=2)
t2 = TextMobject(
"This program made {\\raise.17ex\\hbox{$\\scriptstyle\\sim$}}15,000 calls before crashing."
)
t4 = TextMobject(
"\\textit{Java SE 13.0.1 on macOS Catalina 10.15.4}").scale(0.5)
t2.next_to(t1, DOWN, buff=MED_LARGE_BUFF)
t4.to_edge(DL)
self.play(
FadeIn(t2),
FadeInFromDown(t4),
)
self.wait(duration=4)
t5 = TextMobject('\\textit{Most common mistake with recursion.}')
t6 = TextMobject("You'll see this a lot. Everyone does!")
t6.next_to(t5, DOWN, buff=LARGE_BUFF)
self.play(
*[FadeOut(t) for t in [t1, t2, t4]],
*[FadeIn(t) for t in [t5, t6]],
)
self.wait(duration=3)
# Transition
t1 = TextMobject(
"Alright, let's look at a more interesting function...")
self.play(
*[FadeOut(o) for o in self.mobjects],
FadeIn(t1),
)
self.wait()
self.play(FadeOut(t1))
self.wait()
def construct(self):
title = TextMobject('Quick Review: The Call Stack').to_edge(UP)
code_scale = 0.75
main_code = CodeBlock(
'Java',
r"""
public static
void main(String[] args) {
int n = foo(2);
}
""",
code_scale=code_scale,
)
foo_code = CodeBlock(
'Java',
r"""
static int foo(int x) {
int n = bar(x + 1, x * 2);
return n;
}
""",
code_scale=code_scale,
)
bar_code = CodeBlock(
'Java',
r"""
static int bar(int x,
int y) {
int a = x + y;
return a;
}
""",
code_scale=code_scale,
)
fbg = VGroup(main_code, foo_code, bar_code)
fbg.arrange(DOWN, buff=MED_SMALL_BUFF, aligned_edge=LEFT)
fbg.to_edge(DR)
self.play(
ShowCreation(title),
FadeInFrom(fbg, RIGHT),
)
self.wait()
frame_width = 3.0
args_ref = TextMobject('[ ]').scale(0.5)
main_frame = StackFrame(main_code,
'main()',
3, [('args', args_ref), 'n'],
width=frame_width)
main_frame.next_to(fbg, LEFT, buff=LARGE_BUFF).to_edge(DOWN)
main_code.move_highlight_rect(3)
text_scale = 0.75
b1 = BraceLabel(main_frame,
'The call stack\\\\starts with main()',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
self.play(
FadeInFrom(main_frame, UP),
main_code.highlight_lines,
3,
FadeInFrom(b1, UP),
)
self.wait()
foo_frame = StackFrame(foo_code,
'foo(2)',
5, ['x', 'n'],
width=frame_width)
foo_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
b2 = BraceLabel(foo_frame,
'Calls push frames',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
hr_caller, hr_callee = main_code.setup_for_call(foo_code, 1)
self.play(
main_code.highlight_caller,
ReplacementTransform(hr_caller, hr_callee, path_arc=np.pi),
FadeInFrom(foo_frame, UP),
FadeInFrom(b2, UP),
)
foo_code.complete_callee(hr_callee, self)
self.wait()
self.play(
foo_code.highlight_lines,
2,
foo_frame.set_line,
6,
foo_frame.update_slot,
'x',
2,
)
self.wait()
bar_frame = StackFrame(bar_code,
'bar(3, 4)',
10, ['x', 'y', 'a'],
width=frame_width)
bar_frame.next_to(foo_frame, UP, buff=SMALL_BUFF)
b3 = BraceLabel(bar_frame,
'Holds arguments\\\\and locals',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
hr_caller, hr_callee = foo_code.setup_for_call(bar_code, (1, 2))
self.play(
foo_code.highlight_caller,
ReplacementTransform(hr_caller, hr_callee, path_arc=np.pi),
FadeInFrom(bar_frame, UP),
FadeInFrom(b3, UP),
)
bar_code.complete_callee(hr_callee, self)
self.wait()
self.play(
bar_code.highlight_lines,
3,
bar_frame.set_line,
11,
bar_frame.update_slot,
'x',
3,
bar_frame.update_slot,
'y',
4,
)
self.wait()
self.play(
bar_code.highlight_lines,
4,
bar_frame.set_line,
12,
bar_frame.update_slot,
'a',
7,
)
self.wait(duration=3)
hr_returner, hr_returnee = bar_code.setup_for_return(foo_code)
self.play(
ReplacementTransform(hr_returner, hr_returnee, path_arc=-np.pi),
foo_code.highlight_returnee,
Uncreate(bar_frame),
FadeOutAndShift(b3, LEFT),
FadeOutAndShift(b2, LEFT),
FadeOutAndShift(b1, LEFT),
)
foo_code.complete_returnee(hr_returnee, self)
self.wait()
b4 = BraceLabel(foo_frame,
'Returns pop',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
self.play(
foo_code.highlight_lines,
3,
foo_frame.set_line,
7,
foo_frame.update_slot,
'n',
7,
ShowCreation(b4),
)
self.wait()
hr_returner, hr_returnee = foo_code.setup_for_return(main_code)
self.play(
ReplacementTransform(hr_returner, hr_returnee, path_arc=-np.pi),
main_code.highlight_returnee,
Uncreate(foo_frame),
FadeOutAndShift(b4, LEFT),
)
main_code.complete_returnee(hr_returnee, self)
self.wait()
self.play(
main_code.highlight_lines,
4,
main_frame.set_line,
4,
main_frame.update_slot,
'n',
7,
)
self.wait()
hr_returner, hr_returnee = main_code.setup_for_return(main_code)
hr_returnee.shift(UP * 4)
self.play(
ReplacementTransform(hr_returner, hr_returnee, path_arc=-np.pi),
Uncreate(main_frame),
)
self.remove(hr_returnee)
self.wait()
t1 = TextMobject('Take a moment to think about\\\\'
'where args and locals live,\\\\'
'and what the call stack looks like.').to_edge(LEFT)
t2 = TextMobject('\\textit{It will help later!!}').next_to(
t1, DOWN, buff=LARGE_BUFF)
self.play(FadeIn(t1))
self.wait()
self.play(ShowCreation(t2))
self.wait(duration=2)
def construct(self):
title = TextMobject('The Call Stack').to_edge(UP)
self.add(title)
frame_width = 3.0
dummy_code = CodeBlock('Java', 'foo')
args_ref = TextMobject('[ ]').scale(0.5)
main_frame = StackFrame(dummy_code,
'main()',
3, [('args', args_ref)],
width=frame_width)
foo_frame = StackFrame(dummy_code,
'foo()',
6, [('n', 6)],
width=frame_width)
bar_frame = StackFrame(dummy_code,
'bar(1, 2)',
13, [('x', 1), ('y', 2), ('a', 3), ('b', 6)],
width=frame_width)
main_frame.to_edge(DOWN)
foo_frame.next_to(main_frame, UP)
bar_frame.next_to(foo_frame, UP)
frame_group = VGroup(main_frame, foo_frame, bar_frame)
self.play(
LaggedStartMap(FadeInFrom,
frame_group,
group=frame_group,
direction=UP,
lag_ratio=0.5))
self.wait()
text_scale = 0.75
b1 = BraceLabel(main_frame,
'Always starts\\\\with main()',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
# b2 = BraceLabel(foo_frame, ['Calls push frames,\\\\', 'returns pop'],
# brace_direction=RIGHT, label_constructor=TextMobject,
# alignment='')
b3 = BraceLabel(bar_frame.slots()[0:2],
'Parameters',
brace_direction=RIGHT,
label_constructor=TextMobject,
label_scale=text_scale)
b4 = BraceLabel(bar_frame.slots()[2:4],
'Locals',
brace_direction=RIGHT,
label_constructor=TextMobject,
label_scale=text_scale)
b5 = BraceLabel(bar_frame.slots()[0:4],
'Storage for all\\\\variables in a function',
brace_direction=LEFT,
label_constructor=TextMobject,
label_scale=text_scale)
notes = VGroup(b1, b5, b3, b4)
box_count = 8
colors = color_gradient([BLUE, ORANGE], box_count)
little_boxes = VGroup(*[
Rectangle(height=0.25, width=0.75, fill_opacity=1, color=colors[i])
for i in range(box_count)
])
little_boxes.arrange(UP, buff=0.1)
push_up = TextMobject('Calls push\\\\frames').scale(text_scale)
push_up.next_to(little_boxes, DOWN)
pua = Arrow(push_up.get_bottom(), push_up.get_top()).scale(2)
pua.next_to(push_up, LEFT)
pug = VGroup(push_up, pua)
pop_down = TextMobject('Returns pop\\\\frames').scale(text_scale)
pop_down.next_to(little_boxes, UP)
pda = Arrow(pop_down.get_top(), pop_down.get_bottom()).scale(2)
pda.next_to(pop_down, RIGHT)
pdg = VGroup(pop_down, pda)
bg = VGroup(little_boxes, pug, pdg)
bg.to_edge(RIGHT, buff=MED_LARGE_BUFF)
self.play(
LaggedStartMap(ShowCreation,
notes,
group=notes,
lag_ratio=0.7,
run_time=3.0))
self.play(
FadeIn(pug),
LaggedStartMap(FadeInFrom,
little_boxes,
lambda m: (m, RIGHT),
lag_ratio=1.0,
run_time=3.0))
self.play(FadeIn(pdg))
pdg.generate_target()
pdg.target.next_to(little_boxes[3], UP,
submobject_to_align=pdg[0]).set_opacity(1.0)
self.play(
MoveToTarget(pdg, run_time=3.0),
LaggedStartMap(FadeOutAndShift,
VGroup(*list(reversed(little_boxes))[:4]),
lambda m: (m, RIGHT),
lag_ratio=1.0,
run_time=2.0),
)
self.wait(duration=5)
end_scale_group = VGroup(*self.mobjects)
end_fade_group = VGroup(title)
self.animate_yt_end_screen(end_scale_group,
end_fade_group,
show_elements=False,
show_rects=False)
def construct(self):
title = TextMobject('The Call Stack').to_edge(UP)
t1 = TextMobject("Alright, let's do a more complicated one!")
self.add(title, t1)
self.wait()
code_scale = 0.75
main_code = CodeBlock(
'Java',
r"""
public static
void main(String[] args) {
System.out.println(foo(1));
}
""",
code_scale=code_scale,
)
# Start line: 5
foo_code = CodeBlock(
'Java',
r"""
foo(int a) {
int b = bar(a, 2);
int c = bar(a, b);
return c;
}
""",
code_scale=code_scale,
)
# Start line: 10
bar_code = CodeBlock(
'Java',
r"""
int bar(int x, int y) {
int a = x + y;
int b = a * 2;
return b;
}
""",
code_scale=code_scale,
)
cg = VGroup(main_code, foo_code, bar_code)
cg.arrange(DOWN, aligned_edge=LEFT, buff=MED_SMALL_BUFF)
cg.next_to(title, DOWN, buff=MED_SMALL_BUFF).to_edge(RIGHT)
self.play(
FadeOut(t1),
FadeInFrom(cg, RIGHT),
)
self.wait()
frame_width = 3.0
args_ref = TextMobject('[ ]').scale(0.5)
main_frame = StackFrame(main_code,
'main()',
3, [('args', args_ref)],
width=frame_width)
main_frame.next_to(cg, LEFT, buff=LARGE_BUFF * 2).to_edge(DOWN)
main_code.move_hidden_highlight(3)
self.play(
FadeInFromDown(main_frame),
main_code.highlight_lines,
3,
)
self.wait()
foo_frame = StackFrame(foo_code,
'foo(1)',
5, ['a', 'b', 'c'],
width=frame_width)
foo_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
xi = main_code.pre_call(foo_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(foo_frame, UP),
)
foo_code.post_control_transfer(xi, self)
self.wait()
self.play(foo_code.highlight_lines, 2, foo_frame.set_line, 6,
foo_frame.update_slot, 'a', 1)
self.wait()
bar_frame = StackFrame(bar_code,
'bar(1, 2)',
10, ['x', 'y', 'a', 'b'],
width=frame_width)
bar_frame.next_to(foo_frame, UP, buff=SMALL_BUFF)
xi = foo_code.pre_call(bar_code, 1)
self.play(
*foo_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(bar_frame, UP),
)
bar_code.post_control_transfer(xi, self)
self.wait()
self.play(bar_code.highlight_lines, 2, bar_frame.set_line, 11,
bar_frame.update_slot, 'x', 1, bar_frame.update_slot, 'y', 2)
self.wait()
self.play(bar_code.highlight_lines, 3, bar_frame.set_line, 12,
bar_frame.update_slot, 'a', 3)
self.wait()
self.play(bar_code.highlight_lines, 4, bar_frame.set_line, 13,
bar_frame.update_slot, 'b', 6)
self.wait()
xi = bar_code.pre_return(foo_code, 2)
self.play(
*bar_code.get_control_transfer_clockwise(xi),
Uncreate(bar_frame),
)
foo_code.post_control_transfer(xi, self)
self.wait()
self.play(foo_code.highlight_lines, 3, foo_frame.set_line, 7,
foo_frame.update_slot, 'b', 6)
self.wait()
bar_frame = StackFrame(bar_code,
'bar(1, 6)',
10, ['x', 'y', 'a', 'b'],
width=frame_width)
bar_frame.next_to(foo_frame, UP, buff=SMALL_BUFF)
xi = foo_code.pre_call(bar_code, 1)
self.play(
*foo_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(bar_frame, UP),
)
bar_code.post_control_transfer(xi, self)
self.wait()
self.play(bar_code.highlight_lines, 2, bar_frame.set_line, 11,
bar_frame.update_slot, 'x', 1, bar_frame.update_slot, 'y', 6)
self.wait()
self.play(bar_code.highlight_lines, 3, bar_frame.set_line, 12,
bar_frame.update_slot, 'a', 7)
self.wait()
self.play(bar_code.highlight_lines, 4, bar_frame.set_line, 13,
bar_frame.update_slot, 'b', 14)
self.wait()
xi = bar_code.pre_return(foo_code, 3)
self.play(
*bar_code.get_control_transfer_clockwise(xi),
Uncreate(bar_frame),
)
foo_code.post_control_transfer(xi, self)
self.wait()
self.play(foo_code.highlight_lines, 4, foo_frame.set_line, 8,
foo_frame.update_slot, 'c', 14)
self.wait()
xi = foo_code.pre_return(main_code, 3)
self.play(
*foo_code.get_control_transfer_clockwise(xi),
Uncreate(foo_frame),
)
main_code.post_control_transfer(xi, self)
self.wait()
def fake_frame(name):
frame_name = TextMobject(name).scale(0.75)
br = BackgroundRectangle(frame_name,
buff=SMALL_BUFF,
fill_opacity=0.15)
br.set_fill(color=[ORANGE, BLUE])
return VGroup(frame_name, br)
println_funcs = [
'BufferedWriter.write("14", 0, 2)',
'BufferedWriter(Writer).write("14")',
'PrintStream.writeln("14")',
'PrintStream.println(14)',
]
println_frames = [fake_frame(f) for f in reversed(println_funcs)]
for n, p in zip(println_frames, [main_frame] + println_frames):
n.next_to(p, UP, buff=SMALL_BUFF)
self.play(FadeInFrom(n, UP))
self.wait()
for f in reversed(println_frames):
self.play(Uncreate(f))
# self.wait()
self.play(main_code.highlight_lines, 4, main_frame.set_line, 4)
off_screen_code = CodeBlock('Java', 'off_screen')
off_screen_code.shift(UP * 8) # Offscreen up
self.add(off_screen_code)
xi = main_code.pre_return(off_screen_code, 1)
self.play(
*main_code.get_control_transfer_clockwise(xi),
Uncreate(main_frame),
)
off_screen_code.post_control_transfer(xi, self)
self.wait()
self.play(FadeOut(main_code), FadeOut(foo_code), FadeOut(bar_code))
self.wait()
def construct(self):
high_quality = False
# - Foo calls bar passing some args. Bar does something, returns.
code_scale = 0.75
main_code = CodeBlock(
'Java',
r"""
public static
void main(String[] args) {
foo();
}
""",
code_scale=code_scale,
)
foo_code = CodeBlock(
'Java',
r"""
static int foo() {
int n = bar(1, 2);
return n;
}
""",
code_scale=code_scale,
)
bar_code = CodeBlock(
'Java',
r"""
static int bar(int x,
int y) {
int a = x + y;
int b = a * 2;
return b;
}
""",
code_scale=code_scale,
)
fbg = VGroup(foo_code, bar_code)
bar_code.next_to(foo_code, DOWN, aligned_edge=LEFT, buff=LARGE_BUFF)
fbg.to_edge(TOP)
title = TextMobject('We have two Java functions, foo() and bar()')
title.to_edge(UP)
self.play(
ShowCreation(title),
FadeInFromDown(fbg),
)
self.wait(duration=2)
# Let's write down what happens when we run this.
t2 = TextMobject("Let's run them and write down\\\\"
"each variable as we go...")
t2.to_edge(LEFT)
self.play(Write(t2), fbg.to_edge, RIGHT, {'buff': MED_SMALL_BUFF})
self.wait()
t3 = TextMobject('Running foo() and bar() by hand').to_edge(UP)
if high_quality:
self.play(ReplacementTransform(VGroup(title, t2), t3))
else:
self.play(FadeOut(title), FadeOut(t2), FadeIn(t3))
self.remove(title, t2)
title = t3
self.wait()
t4 = TextMobject('First, make a place\\\\to write each variable')
t4.next_to(title, DOWN, buff=LARGE_BUFF).to_edge(LEFT)
self.play(FadeIn(t4))
self.wait()
foo_vars = VGroup(TexMobject('n:', '\\_'))
foo_vars.next_to(foo_code, LEFT, buff=LARGE_BUFF * 2)
bar_vars = VGroup(
TexMobject('x:', '\\_'),
TexMobject('y:', '\\_').shift(DOWN * .75),
TexMobject('a:', '\\_').shift(DOWN * 1.5),
TexMobject('b:', '\\_').shift(DOWN * 2.25),
)
bar_vars.next_to(bar_code, LEFT, aligned_edge=TOP, buff=LARGE_BUFF * 2)
self.play(Write(foo_vars))
self.play(Write(bar_vars))
self.wait()
t5 = TextMobject("Start in foo()...")
t5.move_to(t4, aligned_edge=LEFT)
self.play(FadeOut(t4), FadeIn(t5))
self.wait()
foo_code.move_hidden_highlight(2)
self.play(FadeOut(t5), foo_code.highlight_lines, 2)
self.wait()
foo_n_q = TexMobject('?').move_to(foo_vars[0][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
self.play(Write(foo_n_q))
foo_vars.add(foo_n_q)
self.wait()
xi = foo_code.pre_call(bar_code, (1, 3))
self.play(*foo_code.get_control_transfer_counterclockwise(xi), )
bar_code.post_control_transfer(xi, self)
self.wait()
bar_x = TexMobject('1').move_to(bar_vars[0][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
bar_y = TexMobject('2').move_to(bar_vars[1][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
a = Arrow(bar_code.get_code().get_lines(2),
VGroup(bar_x, bar_y).get_right(),
stroke_width=3)
self.play(Write(bar_x), Write(bar_y), ShowCreationThenDestruction(a))
bar_vars_extras = VGroup()
bar_vars_extras.add(bar_x, bar_y)
self.play(bar_code.highlight_lines, 3)
self.wait()
bar_a = TexMobject('3').move_to(bar_vars[2][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
a = Arrow(bar_code.get_code().get_lines(3),
bar_a.get_right(),
stroke_width=3)
self.play(Write(bar_a), ShowCreationThenDestruction(a))
bar_vars_extras.add(bar_a)
self.play(bar_code.highlight_lines, 4)
self.wait()
bar_b = TexMobject('6').move_to(bar_vars[3][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
a = Arrow(bar_code.get_code().get_lines(4),
bar_b.get_right(),
stroke_width=3)
self.play(Write(bar_b), ShowCreationThenDestruction(a))
bar_vars_extras.add(bar_b)
self.play(bar_code.highlight_lines, 5)
self.wait()
xi = bar_code.pre_return(foo_code, 2)
self.play(*bar_code.get_control_transfer_clockwise(xi), )
foo_code.post_control_transfer(xi, self)
self.wait()
foo_n = TexMobject('6').move_to(foo_vars[0][1],
aligned_edge=BOTTOM).shift(UP * 0.1)
a = Arrow(foo_code.get_code().get_lines(2),
foo_n.get_right(),
stroke_width=3)
self.play(
foo_code.highlight_lines,
3,
ReplacementTransform(foo_n_q, foo_n),
ShowCreationThenDestruction(a),
)
foo_vars.add(foo_n)
self.wait()
# - Now give the variables "homes" in each function. Variables like
# homes; they're warm and safe and sized just for them!
print('Give variables homes')
t1 = TextMobject('So how does the\\\\computer do this?').to_edge(LEFT)
self.play(FadeIn(t1), foo_code.remove_highlight)
self.wait(duration=2)
t2 = TextMobject(
'Every variable is stored\\\\someplace in memory').to_edge(LEFT)
new_title = TextMobject('Where are variables stored?').to_edge(UP)
self.play(
FadeOut(t1),
FadeOut(title),
FadeIn(new_title),
FadeIn(t2),
)
title = new_title
self.wait()
em = TextMobject('M')
slot_height = em.get_height() + SMALL_BUFF * 2
slot_width = em.get_width() * 4 + SMALL_BUFF * 2
def build_var_home(name, value):
var_name = TextMobject(name)
slot_box = Rectangle(height=slot_height,
width=slot_width,
stroke_width=1)
var_value = TextMobject(value)
var_value.move_to(slot_box)
var_name.next_to(slot_box, LEFT)
stack_slot = VGroup(slot_box, var_name, var_value)
return stack_slot
foo_homes = build_var_home('n', '6')
foo_homes.move_to(foo_vars, aligned_edge=LEFT)
self.play(ReplacementTransform(foo_vars, foo_homes))
self.wait()
bar_var_vals = [('x', '1'), ('y', '2'), ('a', '3'), ('b', '6')]
bar_homes = VGroup()
bar_homes_shift = 0
for n, v in bar_var_vals:
bar_homes.add(build_var_home(n, v).shift(DOWN * bar_homes_shift))
bar_homes_shift += 0.75
bar_homes.move_to(bar_vars, aligned_edge=LEFT)
t3 = TextMobject("Each variable lives in a\\\\``slot''").to_edge(LEFT)
self.play(
ReplacementTransform(bar_vars, bar_homes),
# FadeOut(bar_vars),
FadeOut(bar_vars_extras),
FadeIn(bar_homes),
)
self.wait()
self.play(
FadeOut(t2),
FadeIn(t3),
)
self.wait()
# - Now arrange the homes into a "stack frame".
print('Build stack frames')
t4 = TextMobject(
"All slots for a function\\\\are put together in a\\\\``frame''")
t4.to_edge(LEFT)
self.play(FadeOut(t3), FadeIn(t4))
frame_width = 2.8
foo_vars = [('n', '6')]
foo_frame = StackFrame(foo_code,
'foo()',
3,
foo_vars,
width=frame_width)
foo_frame.move_to(foo_homes, aligned_edge=LEFT).shift(LEFT * .5)
self.play(ReplacementTransform(foo_homes, foo_frame))
self.wait()
bar_frame = StackFrame(bar_code,
'bar(1,2)',
9,
bar_var_vals,
width=frame_width)
bar_frame.move_to(bar_homes, aligned_edge=LEFT).shift(LEFT * .5)
self.play(ReplacementTransform(bar_homes, bar_frame))
self.wait()
t5 = TextMobject("\\textit{They're happy and warm\\\\together!}")\
.scale(0.75).next_to(t4, DOWN, buff=LARGE_BUFF)
self.play(FadeIn(t5))
self.wait()
# Cool, so where do frames live?
print('Where do frames live')
t6 = TextMobject('So where do frames live?').to_edge(LEFT)
self.play(
FadeOut(t5),
FadeOut(t4),
FadeIn(t6),
)
self.wait()
t7 = TextMobject("On the ``call stack''!").next_to(t6,
DOWN,
buff=LARGE_BUFF)
self.play(FadeIn(t7))
self.wait()
new_title = TextMobject('The Call Stack').to_edge(UP)
t1 = TextMobject('Function calls push a new frame\\\\onto the stack')\
.to_edge(LEFT).shift(UP)
t2 = TextMobject('Returning pops a frame off\\\\the stack').next_to(
t1, DOWN, buff=LARGE_BUFF)
box_count = 8
colors = color_gradient([BLUE, ORANGE], box_count)
little_boxes = VGroup(*[
Rectangle(height=0.25, width=0.75, fill_opacity=1, color=colors[i])
for i in range(box_count)
])
little_boxes.arrange(UP, buff=0.1)
little_boxes.next_to(VGroup(foo_code, bar_code), LEFT, buff=LARGE_BUFF)
self.play(
ReplacementTransform(title, new_title),
FadeOut(t6),
FadeOut(t7),
FadeOut(foo_frame),
FadeOut(bar_frame),
FadeIn(t1),
LaggedStartMap(FadeInFrom,
little_boxes,
lambda m: (m, UP),
lag_ratio=1.0,
run_time=4.0),
)
title = new_title
self.wait()
self.play(
FadeIn(t2),
LaggedStartMap(FadeOutAndShift,
VGroup(*reversed(little_boxes)),
lambda m: (m, UP),
lag_ratio=1.0,
run_time=4.0),
)
self.wait(duration=1)
t3 = TextMobject(
"Let's run again and see\\\\the call stack in action...").to_edge(
LEFT)
t3.shift(UP)
self.play(FadeOut(t1), FadeOut(t2), FadeIn(t3))
self.wait()
print('Run with real call stack')
# Let's also put main() into the picture. Start it off-frame upper right
t4 = TextMobject("... and get main()\\\\into the picture.")\
.next_to(t3, DOWN, buff=LARGE_BUFF)
main_code.next_to(title, DOWN, buff=MED_SMALL_BUFF).to_edge(RIGHT)
main_code.shift(UP * 3 + RIGHT * 3)
g = VGroup(main_code, foo_code, bar_code)
self.play(
g.arrange,
DOWN,
{
'aligned_edge': LEFT,
'buff': MED_SMALL_BUFF
},
g.next_to,
title,
DOWN,
{'buff': MED_SMALL_BUFF},
g.to_edge,
RIGHT,
FadeInFromDown(t4),
)
self.wait(duration=2)
t1 = TextMobject('Start in main()...')
t1.next_to(title, DOWN, buff=LARGE_BUFF).to_edge(LEFT)
frame_width = 3.0
args_ref = TextMobject('[ ]').scale(0.5)
main_frame = StackFrame(main_code,
'main()',
3, [('args', args_ref)],
width=frame_width)
main_frame.next_to(g, LEFT, buff=LARGE_BUFF).to_edge(DOWN)
main_code.move_hidden_highlight(3)
self.play(FadeIn(t1), FadeInFromDown(main_frame),
main_code.highlight_lines, 3, FadeOut(t3), FadeOut(t4))
self.wait()
foo_frame = StackFrame(foo_code, 'foo()', 5, ['n'], width=frame_width)
foo_frame.next_to(main_frame, UP, buff=SMALL_BUFF)
b1 = BraceLabel(foo_frame,
'Calling foo()\\\\pushes a frame',
brace_direction=LEFT,
label_constructor=TextMobject)
xi = main_code.pre_call(foo_code, 1)
self.play(
*main_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(foo_frame, UP),
FadeInFrom(b1, UP),
FadeOut(t1),
)
foo_code.post_control_transfer(xi, self)
self.wait(duration=2)
self.play(foo_code.highlight_lines, 2, foo_frame.set_line, 6,
FadeOut(b1))
self.wait()
bar_frame = StackFrame(bar_code,
'bar(1, 2)',
10, ['x', 'y', 'a', 'b'],
width=frame_width)
bar_frame.next_to(foo_frame, UP, buff=SMALL_BUFF)
b1 = BraceLabel(bar_frame,
'Calling bar()\\\\pushes a frame',
brace_direction=LEFT,
label_constructor=TextMobject)
xi = foo_code.pre_call(bar_code, (1, 3))
self.play(
*foo_code.get_control_transfer_counterclockwise(xi),
FadeInFrom(bar_frame, UP),
FadeInFrom(b1, UP),
)
bar_code.post_control_transfer(xi, self)
self.wait()
self.play(bar_frame.update_slot, 'x', 1, bar_frame.update_slot, 'y', 2,
FadeOut(b1))
self.play(bar_code.highlight_lines, 3, bar_frame.set_line, 11)
self.wait()
self.play(bar_frame.update_slot, 'a', 3)
self.play(bar_code.highlight_lines, 4, bar_frame.set_line, 12)
self.wait()
self.play(bar_frame.update_slot, 'b', 6)
self.play(bar_code.highlight_lines, 5, bar_frame.set_line, 13)
b1 = BraceLabel(bar_frame,
"Returning pops\\\\bar's frame",
brace_direction=LEFT,
label_constructor=TextMobject)
self.play(FadeIn(b1))
self.wait(duration=2)
xi = bar_code.pre_return(foo_code, 2)
self.play(
*bar_code.get_control_transfer_clockwise(xi),
Uncreate(bar_frame),
FadeOut(b1),
)
foo_code.post_control_transfer(xi, self)
self.wait()
self.play(foo_code.highlight_lines, 3, foo_frame.set_line, 7,
foo_frame.update_slot, 'n', 6)
b1 = BraceLabel(foo_frame,
"Returning pops\\\\foo's frame",
brace_direction=LEFT,
label_constructor=TextMobject)
self.play(FadeIn(b1))
self.wait()
xi = foo_code.pre_return(main_code, 3)
self.play(
*foo_code.get_control_transfer_clockwise(xi),
Uncreate(foo_frame),
FadeOut(b1),
)
main_code.post_control_transfer(xi, self)
self.wait()
self.play(main_code.highlight_lines, 4, main_frame.set_line, 4)
self.wait()
t1 = TextMobject(
'And when main() returns\\\\the program ends').to_edge(LEFT)
self.play(FadeIn(t1))
self.wait()
off_screen_code = CodeBlock('Java', 'off_screen')
off_screen_code.shift(UP * 8) # Offscreen up
self.add(off_screen_code)
xi = main_code.pre_return(off_screen_code, 1)
self.play(
*main_code.get_control_transfer_clockwise(xi),
Uncreate(main_frame),
FadeOut(t1),
)
off_screen_code.post_control_transfer(xi, self)
self.wait()
t1 = TextMobject("Alright, let's do a more complicated one!")
self.play(
FadeInFromDown(t1),
FadeOutAndShift(g, RIGHT),
)
self.wait()