From 37db664c6cd480b578d6114854bc20c2bc3cddcd Mon Sep 17 00:00:00 2001 From: Rob Pike Date: Mon, 17 Sep 2018 14:25:06 +1000 Subject: [PATCH] builtin: document when len and cap are constant The rules are subtle, but under some circumstances the result can be constant. Mention this and refer to the appropriate section of the specification. Fixes #27588. Change-Id: I4beaad036db87501378fb2ef48d216742d096933 Reviewed-on: https://go-review.googlesource.com/135519 Reviewed-by: Robert Griesemer --- src/builtin/builtin.go | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/src/builtin/builtin.go b/src/builtin/builtin.go index 4578c855a9e..c78fe09ea66 100644 --- a/src/builtin/builtin.go +++ b/src/builtin/builtin.go @@ -152,6 +152,9 @@ func delete(m map[Type]Type1, key Type) // String: the number of bytes in v. // Channel: the number of elements queued (unread) in the channel buffer; // if v is nil, len(v) is zero. +// For some arguments, such as a string literal or a simple array expression, the +// result can be a constant. See the Go language specification's "Length and +// capacity" section for details. func len(v Type) int // The cap built-in function returns the capacity of v, according to its type: @@ -161,6 +164,9 @@ func len(v Type) int // if v is nil, cap(v) is zero. // Channel: the channel buffer capacity, in units of elements; // if v is nil, cap(v) is zero. +// For some arguments, such as a simple array expression, the result can be a +// constant. See the Go language specification's "Length and capacity" section for +// details. func cap(v Type) int // The make built-in function allocates and initializes an object of type