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spec: remove evaluation order inconsistency

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This is a clarification of what happens already.
Not a language change.

Fixes #7137.

LGTM=iant, r, rsc
R=r, rsc, iant, ken
CC=golang-codereviews
https://golang.org/cl/96000044
This commit is contained in:
Robert Griesemer 2014-05-07 08:50:52 -07:00
parent 6f3b84a757
commit dbe5f88804
1 changed files with 31 additions and 6 deletions
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37
doc/go_spec.html
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@ -3996,8 +3996,11 @@ precision.
<h3 id="Order_of_evaluation">Order of evaluation</h3>
<p>
When evaluating the <a href="#Operands">operands</a> of an expression,
<a href="#Assignments">assignment</a>, or
At package level, <a href="#Program_execution"</a>initialization dependencies</a>
determine the evaluation order of individual initialization expressions in
<a href="#Variable_declarations">variable declarations</a>.
Otherwise, when evaluating the <a href="#Operands">operands</a> of an
expression, assignment, or
<a href="#Return_statements">return statement</a>,
all function calls, method calls, and
communication operations are evaluated in lexical left-to-right
@ -4005,7 +4008,7 @@ order.
</p>
<p>
For example, in the assignment
For example, in the (function-local) assignment
</p>
<pre>
y[f()], ok = g(h(), i()+x[j()], &lt;-c), k()
@ -4022,11 +4025,33 @@ of <code>y</code> is not specified.
<pre>
a := 1
f := func() int { a++; return a }
x := []int{a, f()} // x may be [1, 2] or [2, 2]: evaluation order between a and f() is not specified
m := map[int]int{a: 1, a: 2} // m may be {2: 1} or {2: 2}: evaluation order between the two map assignments is not specified
m2 := map[int]int{a: f()} // m2 may be {2: 3} or {3: 3}: evaluation order between the key and the value is not specified
x := []int{a, f()} // x may be [1, 2] or [2, 2]: evaluation order between a and f() is not specified
m := map[int]int{a: 1, a: 2} // m may be {2: 1} or {2: 2}: evaluation order between the two map assignments is not specified
n := map[int]int{a: f()} // n may be {2: 3} or {3: 3}: evaluation order between the key and the value is not specified
</pre>
<p>
At package level, initialization dependencies override the left-to-right rule
for individual initialization expressions, but not for operands within each
expression:
</p>
<pre>
var a, b, c = f() + v(), g(), sqr(u()) + v()
func f() int { return c }
func g() int { return a }
func sqr(x int) int { return x*x }
// functions u and v are independent of all other variables and functions
</pre>
<p>
The function calls happen in the order
<code>u()</code>, <code>sqr()</code>, <code>v()</code>,
<code>f()</code>, <code>v()</code>, and <code>g()</code>.
</p>
<p>
Floating-point operations within a single expression are evaluated according to
the associativity of the operators. Explicit parentheses affect the evaluation