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langref: new usingnamespace semantics

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This commit is contained in:
Andrew Kelley
2021-08-31 17:01:57 -07:00
parent f4d3d29f92
commit feec4b0614
1 changed files with 8 additions and 19 deletions
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27
doc/langref.html.in
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@@ -5812,32 +5812,20 @@ test "@intToPtr for pointer to zero bit type" {
{#header_open|usingnamespace#}
<p>
{#syntax#}usingnamespace{#endsyntax#} is a declaration that imports all the public declarations of
the operand, which must be a {#link|struct#}, {#link|union#}, or {#link|enum#}, into the current scope:
{#syntax#}usingnamespace{#endsyntax#} is a declaration that mixes all the public
declarations of the operand, which must be a {#link|struct#}, {#link|union#}, {#link|enum#},
or {#link|opaque#}, into the namespace:
</p>
{#code_begin|test|usingnamespace#}
usingnamespace @import("std");
test "using std namespace" {
try testing.expect(true);
}
{#code_end#}
<p>
{#syntax#}usingnamespace{#endsyntax#} can also be used in containers:
</p>
{#code_begin|test|usingnamespace_inside_struct#}
test "using namespace inside struct" {
const L = struct {
usingnamespace struct {
pub fn f() void {}
};
const S = struct {
usingnamespace @import("std");
};
L.f();
try S.testing.expect(true);
}
{#code_end#}
<p>
Instead of the above pattern, it is generally recommended to explicitly alias individual declarations.
However, {#syntax#}usingnamespace{#endsyntax#} has an important use case when organizing the public
{#syntax#}usingnamespace{#endsyntax#} has an important use case when organizing the public
API of a file or package. For example, one might have <code>c.zig</code> with all of the
{#link|C imports|Import from C Header File#}:
</p>
@@ -5858,6 +5846,7 @@ pub usingnamespace @cImport({
</p>
{#header_close#}
{#header_open|comptime#}
<p>
Zig places importance on the concept of whether an expression is known at compile-time.