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Document sentinel type in langref #3861

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Dec 13, 2019
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Document sentinel type in langref #3861

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20 changes: 20 additions & 0 deletions doc/langref.html.in
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Original file line number Diff line number Diff line change
Expand Up @@ -8351,6 +8351,7 @@ pub const TypeInfo = union(TypeId) {
alignment: comptime_int,
child: type,
is_allowzero: bool,
sentinel: var,

pub const Size = enum {
One,
Expand All @@ -8363,6 +8364,7 @@ pub const TypeInfo = union(TypeId) {
pub const Array = struct {
len: comptime_int,
child: type,
sentinel: var,
};

pub const ContainerLayout = enum {
Expand Down Expand Up @@ -8493,6 +8495,24 @@ pub const TypeInfo = union(TypeId) {
{#link|error sets|Error Set Type#}, the fields are guaranteed to be in the same
order as declared. For declarations, the order is unspecified.
</p>
<p>
Note that the {#syntax#}sentinel{#endsyntax#} field in {#syntax#}TypeInfo.Pointer{#endsyntax#}
and {#syntax#}TypeInfo.Array{#endsyntax#} is of type {#syntax#}var{#endsyntax#} rather
than {#syntax#}?child{#endsyntax#}. {#syntax#}TypeInfo.Pointer{#endsyntax#}
and {#syntax#}TypeInfo.Array{#endsyntax#} can be constructed with any comptime value for the
{#syntax#}sentinel{#endsyntax#} field. However, the {#syntax#}@Type{#endsyntax#} builtin will
only accept the TypeInfo struct if the sentinel value is implicitly convertible to
{#syntax#}child{#endsyntax#}. Furthermore, any {#syntax#}TypeInfo.Pointer{#endsyntax#}
or {#syntax#}TypeInfo.Array{#endsyntax#} retreived from {#syntax#}@typeInfo{#endsyntax#} will
guarantee that {#syntax#}@typeOf(sentinel){#endsyntax#} is equal to
{#syntax#}?child{#endsyntax#}. For example, {#syntax#}@typeOf(sentinel){#endsyntax#} for a
{#syntax#}TypeInfo.Pointer{#endsyntax#} constructed with
{#syntax#}TypeInfo.Pointer { ... .sentinel = 0; ... }{#endsyntax#} would be
{#syntax#}comptime_int{#endsyntax#} rather than {#syntax#}?u8{#endsyntax#}. However, if you
passed that {#syntax#}TypeInfo.Pointer{#endsyntax#} struct to
{#syntax#}@typeInfo(@Type(myPointerInfo)){#endsyntax#} then {#syntax#}@typeOf(sentinel){#endsyntax#}
would be {#syntax#}?u8{#endsyntax#}.
</p>
{#header_close#}

{#header_open|@typeName#}
Expand Down