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revert langref section "common errdefer slip ups"

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This does not belong in the language reference.

reverts 91a88a789f
This commit is contained in:
Andrew Kelley 2024-11-26 15:03:24 -08:00
parent 11bf2d92de
commit 3ce6de8765
5 changed files with 0 additions and 178 deletions
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26
doc/langref.html.in
View file

@ -3052,32 +3052,6 @@ fn createFoo(param: i32) !Foo {
The {#syntax#}errdefer{#endsyntax#} statement can optionally capture the error:
</p>
{#code|test_errdefer_capture.zig#}
{#header_close#}
{#header_open|Common errdefer Slip-Ups#}
<p>
It should be noted that {#syntax#}errdefer{#endsyntax#} statements only last until the end of the block
they are written in, and therefore are not run if an error is returned outside of that block:
</p>
{#code|test_errdefer_slip_ups.zig#}
<p>
To ensure that {#syntax#}deallocateFoo{#endsyntax#} is properly called
when returning an error, you must add an {#syntax#}errdefer{#endsyntax#} outside of the block:
</p>
{#code|test_errdefer_block.zig#}
<p>
The fact that errdefers only last for the block they are declared in is
especially important when using loops:
</p>
{#code|test_errdefer_loop_leak.zig#}
<p>
Special care must be taken with code that allocates in a loop
to make sure that no memory is leaked when returning an error:
</p>
{#code|test_errdefer_loop.zig#}
{#header_close#}
<p>
A couple of other tidbits about error handling:

42
doc/langref/test_errdefer_block.zig
View file

@ -1,42 +0,0 @@
const std = @import("std");
const Allocator = std.mem.Allocator;
const Foo = struct {
data: u32,
};
fn tryToAllocateFoo(allocator: Allocator) !*Foo {
return allocator.create(Foo);
}
fn deallocateFoo(allocator: Allocator, foo: *Foo) void {
allocator.destroy(foo);
}
fn getFooData() !u32 {
return 666;
}
fn createFoo(allocator: Allocator, param: i32) !*Foo {
const foo = getFoo: {
var foo = try tryToAllocateFoo(allocator);
errdefer deallocateFoo(allocator, foo);
foo.data = try getFooData();
break :getFoo foo;
};
// This lasts for the rest of the function
errdefer deallocateFoo(allocator, foo);
// Error is now properly handled by errdefer
if (param > 1337) return error.InvalidParam;
return foo;
}
test "createFoo" {
try std.testing.expectError(error.InvalidParam, createFoo(std.testing.allocator, 2468));
}
// test

36
doc/langref/test_errdefer_loop.zig
View file

@ -1,36 +0,0 @@
const std = @import("std");
const Allocator = std.mem.Allocator;
const Foo = struct { data: *u32 };
fn getData() !u32 {
return 666;
}
fn genFoos(allocator: Allocator, num: usize) ![]Foo {
const foos = try allocator.alloc(Foo, num);
errdefer allocator.free(foos);
// Used to track how many foos have been initialized
// (including their data being allocated)
var num_allocated: usize = 0;
errdefer for (foos[0..num_allocated]) |foo| {
allocator.destroy(foo.data);
};
for (foos, 0..) |*foo, i| {
foo.data = try allocator.create(u32);
num_allocated += 1;
if (i >= 3) return error.TooManyFoos;
foo.data.* = try getData();
}
return foos;
}
test "genFoos" {
try std.testing.expectError(error.TooManyFoos, genFoos(std.testing.allocator, 5));
}
// test

32
doc/langref/test_errdefer_loop_leak.zig
View file

@ -1,32 +0,0 @@
const std = @import("std");
const Allocator = std.mem.Allocator;
const Foo = struct { data: *u32 };
fn getData() !u32 {
return 666;
}
fn genFoos(allocator: Allocator, num: usize) ![]Foo {
const foos = try allocator.alloc(Foo, num);
errdefer allocator.free(foos);
for (foos, 0..) |*foo, i| {
foo.data = try allocator.create(u32);
// This errdefer does not last between iterations
errdefer allocator.destroy(foo.data);
// The data for the first 3 foos will be leaked
if (i >= 3) return error.TooManyFoos;
foo.data.* = try getData();
}
return foos;
}
test "genFoos" {
try std.testing.expectError(error.TooManyFoos, genFoos(std.testing.allocator, 5));
}
// test_error=3 errors were logged

42
doc/langref/test_errdefer_slip_ups.zig
View file

@ -1,42 +0,0 @@
const std = @import("std");
const Allocator = std.mem.Allocator;
const Foo = struct {
data: u32,
};
fn tryToAllocateFoo(allocator: Allocator) !*Foo {
return allocator.create(Foo);
}
fn deallocateFoo(allocator: Allocator, foo: *Foo) void {
allocator.destroy(foo);
}
fn getFooData() !u32 {
return 666;
}
fn createFoo(allocator: Allocator, param: i32) !*Foo {
const foo = getFoo: {
var foo = try tryToAllocateFoo(allocator);
errdefer deallocateFoo(allocator, foo); // Only lasts until the end of getFoo
// Calls deallocateFoo on error
foo.data = try getFooData();
break :getFoo foo;
};
// Outside of the scope of the errdefer, so
// deallocateFoo will not be called here
if (param > 1337) return error.InvalidParam;
return foo;
}
test "createFoo" {
try std.testing.expectError(error.InvalidParam, createFoo(std.testing.allocator, 2468));
}
// test_error=1 tests leaked memory