hasUniqueRepresentation

True if every value of the type T has a unique bit pattern representing it. In other words, T has no unused bits and no padding. Result is always comptime-known.

Function parameters

Parameters

T:type

Functions in this namespace

Functions

TrailerFlags
stringToEnum: Returns the variant of an enum type, `T`, which is named `str`, or `null` if no such variant exists.
alignment: Returns the alignment of type T.
Child: Given a parameterized type (array, vector, pointer, optional), returns the "child type".
Elem: Given a "memory span" type (array, slice, vector, or pointer to such), returns the "element type".
sentinel: Given a type which can have a sentinel e.g.
Sentinel: Given a "memory span" type, returns the same type except with the given sentinel value.
containerLayout
declarations: Instead of this function, prefer to use e.g.
declarationInfo
fields
fieldInfo
fieldNames
tags: Given an enum or error set type, returns a pointer to an array containing all tags for that
FieldEnum: Returns an enum with a variant named after each field of `T`.
DeclEnum
Tag
activeTag: Returns the active tag of a tagged union
TagPayloadByName: Deprecated: Use @FieldType(U, tag_name)
TagPayload: Deprecated: Use @FieldType(U, @tagName(tag))
eql: Compares two of any type for equality.
intToEnum: Deprecated: use `std.enums.fromInt` instead and handle null instead of an error.
fieldIndex: Given a type and a name, return the field index according to source order.
declList: Returns a slice of pointers to public declarations of a namespace.
Int
Float
ArgsTuple: For a given function type, returns a tuple type which fields will
Tuple: For a given anonymous list of types, returns a new tuple type
isError: Returns whether `error_union` contains an error.
hasFn: Returns true if a type has a namespace and the namespace contains `name`;
hasMethod: Returns true if a type has a `name` method; `false` otherwise.
hasUniqueRepresentation: True if every value of the type `T` has a unique bit pattern representing it.

Error sets in this namespace

Error Sets

IntToEnumError: Deprecated: use `std.enums.fromInt` instead and handle null.

Source

Implementation

pub inline fn hasUniqueRepresentation(comptime T: type) bool {
    return switch (@typeInfo(T)) {
        else => false, // TODO can we know if it's true for some of these types ?

        .@"anyframe",
        .@"enum",
        .error_set,
        .@"fn",
        => true,

        .bool => false,

        .int => |info| @sizeOf(T) * 8 == info.bits,

        .pointer => |info| info.size != .slice,

        .optional => |info| switch (@typeInfo(info.child)) {
            .pointer => |ptr| !ptr.is_allowzero and switch (ptr.size) {
                .slice, .c => false,
                .one, .many => true,
            },
            else => false,
        },

        .array => |info| hasUniqueRepresentation(info.child),

        .@"struct" => |info| {
            if (info.layout == .@"packed") return @sizeOf(T) * 8 == @bitSizeOf(T);

            var sum_size = @as(usize, 0);

            inline for (info.fields) |field| {
                if (field.is_comptime) continue;
                if (!hasUniqueRepresentation(field.type)) return false;
                sum_size += @sizeOf(field.type);
            }

            return @sizeOf(T) == sum_size;
        },

        .vector => |info| hasUniqueRepresentation(info.child) and
            @sizeOf(T) == @sizeOf(info.child) * info.len,
    };
}