From f49a757ad0d8f5987953684ea20153c713f7d9b9 Mon Sep 17 00:00:00 2001 From: Ian Lance Taylor Date: Tue, 26 Jan 2016 17:23:33 -0800 Subject: [PATCH] unsafe: clarify that Alignof returns required alignment Also document the special behavior of Alignof(s.f), and mention the correspondence between Alignof and reflect.Type.{Align,FieldAlign}. Change-Id: I6f81047a04c86887f1b1164473225616cae45a26 Reviewed-on: https://go-review.googlesource.com/18949 Run-TryBot: Ian Lance Taylor Reviewed-by: Russ Cox --- src/unsafe/unsafe.go | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/src/unsafe/unsafe.go b/src/unsafe/unsafe.go index 34ca77965b..3c8cd34ae2 100644 --- a/src/unsafe/unsafe.go +++ b/src/unsafe/unsafe.go @@ -183,7 +183,12 @@ func Sizeof(x ArbitraryType) uintptr // number of bytes between the start of the struct and the start of the field. func Offsetof(x ArbitraryType) uintptr -// Alignof takes an expression x of any type and returns the alignment +// Alignof takes an expression x of any type and returns the required alignment // of a hypothetical variable v as if v was declared via var v = x. -// It is the largest value m such that the address of v is zero mod m. +// It is the largest value m such that the address of v is always zero mod m. +// It is the same as the value returned by reflect.TypeOf(x).Align(). +// As a special case, if s has a struct type and f is a field within that +// struct, then Alignof(s.f) will return the required alignment of a field +// of that type within a struct. This case is the same as the value returned +// by reflect.TypeOf(s.f).FieldAlign(). func Alignof(x ArbitraryType) uintptr -- 2.48.1