pub fn assert(ok: bool) voidInvokes detectable illegal behavior when ok is false.
In debug and safe modes, calls to this function are always generated, and the unreachable statement triggers a panic.
In fast and small modes, calls to this function are optimized away, and in fact the optimizer is able to use the assertion in its heuristics.
Inside a test block, it is best to use the testing module rather than this function, because this function may not detect a test failure in fast and small mode. Outside of a test block, this assert function is the correct function to use.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165const std = @import("../std.zig");
const meta = std.meta;
const testing = std.testing;
const mem = std.mem;
const assert = std.debug.assert;
const Type = std.builtin.Type;
/// This is useful for saving memory when allocating an object that has many
/// optional components. The optional objects are allocated sequentially in
/// memory, and a single integer is used to represent each optional object
/// and whether it is present based on each corresponding bit.
pub fn TrailerFlags(comptime Fields: type) type {
return struct {
bits: Int,
pub const Int = @Int(.unsigned, bit_count);
pub const bit_count = @typeInfo(Fields).@"struct".field_names.len;
pub const FieldEnum = std.meta.FieldEnum(Fields);
pub const ActiveFields = std.enums.EnumFieldStruct(FieldEnum, bool, false);
pub const FieldValues = blk: {
var field_names: [bit_count][]const u8 = undefined;
var field_types: [bit_count]type = undefined;
var field_attrs: [bit_count]std.builtin.Type.Struct.FieldAttributes = undefined;
const fields_info = @typeInfo(Fields).@"struct";
for (
fields_info.field_names,
fields_info.field_types,
&field_names,
&field_types,
&field_attrs,
) |field_name, field_type, *new_name, *NewType, *new_attrs| {
new_name.* = field_name;
NewType.* = ?field_type;
const default: ?field_type = null;
new_attrs.* = .{ .default_value_ptr = &default };
}
break :blk @Struct(.auto, null, &field_names, &field_types, &field_attrs);
};
const Self = @This();
pub fn has(self: Self, comptime field: FieldEnum) bool {
const field_index = @backingInt(field);
return (self.bits & (1 << field_index)) != 0;
}
pub fn get(self: Self, p: [*]align(@alignOf(Fields)) const u8, comptime field: FieldEnum) ?Field(field) {
if (!self.has(field))
return null;
return self.ptrConst(p, field).*;
}
pub fn setFlag(self: *Self, comptime field: FieldEnum) void {
const field_index = @backingInt(field);
self.bits |= 1 << field_index;
}
/// `fields` is a boolean struct where each active field is set to `true`
pub fn init(fields: ActiveFields) Self {
var self: Self = .{ .bits = 0 };
inline for (@typeInfo(Fields).@"struct".field_names, 0..) |field_name, i| {
if (@field(fields, field_name))
self.bits |= 1 << i;
}
return self;
}
/// `fields` is a struct with each field set to an optional value
pub fn setMany(self: Self, p: [*]align(@alignOf(Fields)) u8, fields: FieldValues) void {
inline for (@typeInfo(Fields).@"struct".field_names, 0..) |field_name, i| {
if (@field(fields, field_name)) |value|
self.set(p, @as(FieldEnum, @fromBackingInt(@intCast(i))), value);
}
}
pub fn set(
self: Self,
p: [*]align(@alignOf(Fields)) u8,
comptime field: FieldEnum,
value: Field(field),
) void {
self.ptr(p, field).* = value;
}
pub fn ptr(self: Self, p: [*]align(@alignOf(Fields)) u8, comptime field: FieldEnum) *Field(field) {
if (@sizeOf(Field(field)) == 0)
return undefined;
const off = self.offset(field);
return @ptrCast(@alignCast(p + off));
}
pub fn ptrConst(self: Self, p: [*]align(@alignOf(Fields)) const u8, comptime field: FieldEnum) *const Field(field) {
if (@sizeOf(Field(field)) == 0)
return undefined;
const off = self.offset(field);
return @ptrCast(@alignCast(p + off));
}
pub fn offset(self: Self, comptime field: FieldEnum) usize {
var off: usize = 0;
inline for (@typeInfo(Fields).@"struct".field_types, 0..) |field_type, i| {
const active = (self.bits & (1 << i)) != 0;
if (i == @backingInt(field)) {
assert(active);
return mem.alignForward(usize, off, @alignOf(field_type));
} else if (active) {
off = mem.alignForward(usize, off, @alignOf(field_type));
off += @sizeOf(field_type);
}
}
}
pub fn Field(comptime field: FieldEnum) type {
return @typeInfo(Fields).@"struct".field_types[@backingInt(field)];
}
pub fn sizeInBytes(self: Self) usize {
var off: usize = 0;
inline for (@typeInfo(Fields).@"struct".field_types, 0..) |field_type, i| {
if (@sizeOf(field_type) == 0)
continue;
if ((self.bits & (1 << i)) != 0) {
off = mem.alignForward(usize, off, @alignOf(field_type));
off += @sizeOf(field_type);
}
}
return off;
}
};
}
test TrailerFlags {
const Flags = TrailerFlags(struct {
a: i32,
b: bool,
c: u64,
});
try testing.expectEqual(u2, meta.Tag(Flags.FieldEnum));
var flags = Flags.init(.{
.b = true,
.c = true,
});
const slice = try testing.allocator.alignedAlloc(u8, .@"8", flags.sizeInBytes());
defer testing.allocator.free(slice);
flags.set(slice.ptr, .b, false);
flags.set(slice.ptr, .c, 12345678);
try testing.expect(flags.get(slice.ptr, .a) == null);
try testing.expect(!flags.get(slice.ptr, .b).?);
try testing.expect(flags.get(slice.ptr, .c).? == 12345678);
flags.setMany(slice.ptr, .{
.b = true,
.c = 5678,
});
try testing.expect(flags.get(slice.ptr, .a) == null);
try testing.expect(flags.get(slice.ptr, .b).?);
try testing.expect(flags.get(slice.ptr, .c).? == 5678);
}