| ... | ... | @@ -6665,6 +6665,8 @@ comptime { |
| 6665 | 6665 | {#code_end#} |
| 6666 | 6666 | <p>At runtime:</p> |
| 6667 | 6667 | {#code_begin|exe_err#} |
| 6668 | const std = @import("std"); |
| 6669 | |
| 6668 | 6670 | const Set1 = error{ |
| 6669 | 6671 | A, |
| 6670 | 6672 | B, |
| ... | ... | @@ -6674,10 +6676,11 @@ const Set2 = error{ |
| 6674 | 6676 | C, |
| 6675 | 6677 | }; |
| 6676 | 6678 | pub fn main() void { |
| 6677 | | _ = foo(Set1.B); |
| 6679 | foo(Set1.B); |
| 6678 | 6680 | } |
| 6679 | | fn foo(set1: Set1) Set2 { |
| 6680 | | return @errSetCast(Set2, set1); |
| 6681 | fn foo(set1: Set1) void { |
| 6682 | const x = @errSetCast(Set2, set1); |
| 6683 | std.debug.warn("value: {}\n", x); |
| 6681 | 6684 | } |
| 6682 | 6685 | {#code_end#} |
| 6683 | 6686 | {#header_close#} |
| ... | ... | @@ -6705,7 +6708,84 @@ fn foo(bytes: []u8) u32 { |
| 6705 | 6708 | {#code_end#} |
| 6706 | 6709 | {#header_close#} |
| 6707 | 6710 | {#header_open|Wrong Union Field Access#} |
| 6708 | | <p>TODO</p> |
| 6711 | <p>At compile-time:</p> |
| 6712 | {#code_begin|test_err|accessing union field 'float' while field 'int' is set#} |
| 6713 | comptime { |
| 6714 | var f = Foo{ .int = 42 }; |
| 6715 | f.float = 12.34; |
| 6716 | } |
| 6717 | |
| 6718 | const Foo = union { |
| 6719 | float: f32, |
| 6720 | int: u32, |
| 6721 | }; |
| 6722 | {#code_end#} |
| 6723 | <p>At runtime:</p> |
| 6724 | {#code_begin|exe_err#} |
| 6725 | const std = @import("std"); |
| 6726 | |
| 6727 | const Foo = union { |
| 6728 | float: f32, |
| 6729 | int: u32, |
| 6730 | }; |
| 6731 | |
| 6732 | pub fn main() void { |
| 6733 | var f = Foo{ .int = 42 }; |
| 6734 | bar(&f); |
| 6735 | } |
| 6736 | |
| 6737 | fn bar(f: *Foo) void { |
| 6738 | f.float = 12.34; |
| 6739 | std.debug.warn("value: {}\n", f.float); |
| 6740 | } |
| 6741 | {#code_end#} |
| 6742 | <p> |
| 6743 | This safety is not available for <code>extern</code> or <code>packed</code> unions. |
| 6744 | </p> |
| 6745 | <p> |
| 6746 | To change the active field of a union, assign the entire union, like this: |
| 6747 | </p> |
| 6748 | {#code_begin|exe#} |
| 6749 | const std = @import("std"); |
| 6750 | |
| 6751 | const Foo = union { |
| 6752 | float: f32, |
| 6753 | int: u32, |
| 6754 | }; |
| 6755 | |
| 6756 | pub fn main() void { |
| 6757 | var f = Foo{ .int = 42 }; |
| 6758 | bar(&f); |
| 6759 | } |
| 6760 | |
| 6761 | fn bar(f: *Foo) void { |
| 6762 | f.* = Foo{ .float = 12.34 }; |
| 6763 | std.debug.warn("value: {}\n", f.float); |
| 6764 | } |
| 6765 | {#code_end#} |
| 6766 | <p> |
| 6767 | To change the active field of a union when a meaningful value for the field is not known, |
| 6768 | use {#link|undefined#}, like this: |
| 6769 | </p> |
| 6770 | {#code_begin|exe#} |
| 6771 | const std = @import("std"); |
| 6772 | |
| 6773 | const Foo = union { |
| 6774 | float: f32, |
| 6775 | int: u32, |
| 6776 | }; |
| 6777 | |
| 6778 | pub fn main() void { |
| 6779 | var f = Foo{ .int = 42 }; |
| 6780 | f = Foo{ .float = undefined }; |
| 6781 | bar(&f); |
| 6782 | std.debug.warn("value: {}\n", f.float); |
| 6783 | } |
| 6784 | |
| 6785 | fn bar(f: *Foo) void { |
| 6786 | f.float = 12.34; |
| 6787 | } |
| 6788 | {#code_end#} |
| 6709 | 6789 | {#header_close#} |
| 6710 | 6790 | |
| 6711 | 6791 | {#header_open|Out of Bounds Float To Integer Cast#} |
Andrew Kelley <andrew@ziglang.org> 2018-07-10 10:37:58-04:00