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go spec: define make() restrictions as for index expressions

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This is a language change: Until now, the spec required run-
time panics for some of these errors. Note that gc and gccgo
implemented this inconsistently, and that both compilers already
reported compile-time errors in some cases. This change makes
make() behave along the same vein as index expressions.

This addresses the spec aspect of issue 4085.

R=r, rsc, iant, ken
CC=golang-dev
https://golang.org/cl/6725053
This commit is contained in:
Robert Griesemer 2012-10-19 10:11:06 -07:00
parent c117da37a2
commit 3bde00033b
1 changed files with 9 additions and 6 deletions
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15
doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification",
"Subtitle": "Version of October 17, 2012",
"Subtitle": "Version of October 19, 2012",
"Path": "/ref/spec"
}-->
@ -4920,15 +4920,18 @@ make(T, n) channel asynchronous channel of type T, buffer size n
<p>
The arguments <code>n</code> and <code>m</code> must be of integer type.
A <a href="#Run_time_panics">run-time panic</a> occurs if <code>n</code>
is negative or larger than <code>m</code>, or if <code>n</code> or
<code>m</code> cannot be represented by an <code>int</code>.
The size arguments <code>n</code> and <code>m</code> must be integer values.
A <a href="#Constants">constant</a> size argument must not be negative, and
if both <code>n</code> and <code>m</code> are provided and are constant, then
<code>n</code> must be no larger than <code>m</code>.
If <code>n</code> is negative or larger than <code>m</code> at run time,
a <a href="#Run_time_panics">run-time panic</a> occurs.
</p>
<pre>
s := make([]int, 10, 100) // slice with len(s) == 10, cap(s) == 100
s := make([]int, 10) // slice with len(s) == cap(s) == 10
s := make([]int, 1e3) // slice with len(s) == cap(s) == 1000
s := make([]int, 10, 0) // illegal: len(s) > cap(s)
c := make(chan int, 10) // channel with a buffer size of 10
m := make(map[string]int, 100) // map with initial space for 100 elements
</pre>