| ... | ... | @@ -5370,6 +5370,44 @@ test "fn type inference" { |
| 5370 | 5370 | {#code_end#} |
| 5371 | 5371 | |
| 5372 | 5372 | {#header_close#} |
| 5373 | |
| 5374 | {#header_open|inline fn#} |
| 5375 | <p> |
| 5376 | Adding the {#syntax#}inline{#endsyntax#} keyword to a function definition makes that |
| 5377 | function become <em>semantically inlined</em> at the callsite. This is |
| 5378 | not a hint to be possibly observed by optimization passes, but has |
| 5379 | implications on the types and values involved in the function call. |
| 5380 | </p> |
| 5381 | <p> |
| 5382 | Unlike normal function calls, arguments at an inline function callsite which are |
| 5383 | compile-time known are treated as {#link|Compile Time Parameters#}. This can potentially |
| 5384 | propagate all the way to the return value: |
| 5385 | </p> |
| 5386 | {#code_begin|test|inline_call#} |
| 5387 | test "inline function call" { |
| 5388 | if (foo(1200, 34) != 1234) { |
| 5389 | @compileError("bad"); |
| 5390 | } |
| 5391 | } |
| 5392 | |
| 5393 | inline fn foo(a: i32, b: i32) i32 { |
| 5394 | return a + b; |
| 5395 | } |
| 5396 | {#code_end#} |
| 5397 | <p>If {#syntax#}inline{#endsyntax#} is removed, the test fails with the compile error |
| 5398 | instead of passing.</p> |
| 5399 | <p>It is generally better to let the compiler decide when to inline a |
| 5400 | function, except for these scenarios:</p> |
| 5401 | <ul> |
| 5402 | <li>To change how many stack frames are in the call stack, for debugging purposes.</li> |
| 5403 | <li>To force comptime-ness of the arguments to propagate to the return value of the function, as in the above example.</i> |
| 5404 | <li>Real world performance measurements demand it.</li> |
| 5405 | </ul> |
| 5406 | <p>Note that {#syntax#}inline{#endsyntax#} actually <em>restricts</em> |
| 5407 | what the compiler is allowed to do. This can harm binary size, |
| 5408 | compilation speed, and even runtime performance.</p> |
| 5409 | {#header_close#} |
| 5410 | |
| 5373 | 5411 | {#header_open|Function Reflection#} |
| 5374 | 5412 | {#code_begin|test|test_fn_reflection#} |
| 5375 | 5413 | const std = @import("std"); |
Andrew Kelley <andrew@ziglang.org> 2024-01-10 19:31:28-07:00