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Use ComptimeStringMap in std.meta.stringToEnum when feasible

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This commit is contained in:
Ryan Liptak 2020-05-26 22:31:36 -07:00
parent dfafafac7b
commit b683498ae8
1 changed files with 29 additions and 4 deletions
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33
lib/std/meta.zig
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@ -53,12 +53,37 @@ test "std.meta.tagName" {
}
pub fn stringToEnum(comptime T: type, str: []const u8) ?T {
inline for (@typeInfo(T).Enum.fields) |enumField| {
if (mem.eql(u8, str, enumField.name)) {
return @field(T, enumField.name);
// Using ComptimeStringMap here is more performant, but it will start to take too
// long to compile if the enum is large enough, due to the current limits of comptime
// performance when doing things like constructing lookup maps at comptime.
// TODO The '100' here is arbitrary and should be increased when possible:
// - https://github.com/ziglang/zig/issues/4055
// - https://github.com/ziglang/zig/issues/3863
if (@typeInfo(T).Enum.fields.len <= 100) {
const kvs = comptime build_kvs: {
// In order to generate an array of structs that play nice with anonymous
// list literals, we need to give them "0" and "1" field names.
// TODO https://github.com/ziglang/zig/issues/4335
const EnumKV = struct {
@"0": []const u8,
@"1": T,
};
var kvs_array: [@typeInfo(T).Enum.fields.len]EnumKV = undefined;
inline for (@typeInfo(T).Enum.fields) |enumField, i| {
kvs_array[i] = .{.@"0" = enumField.name, .@"1" = @field(T, enumField.name)};
}
break :build_kvs kvs_array[0..];
};
const map = std.ComptimeStringMap(T, kvs);
return map.get(str);
} else {
inline for (@typeInfo(T).Enum.fields) |enumField| {
if (mem.eql(u8, str, enumField.name)) {
return @field(T, enumField.name);
}
}
return null;
}
return null;
}
test "std.meta.stringToEnum" {