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spec: function invocation, panic on *nil

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Document that indirection through a nil pointer will panic.
Explain function invocation.
This section will need more work, but it's a start.

Fixes #1865.
Fixes #2252.

R=rsc, iant, r
CC=golang-dev
https://golang.org/cl/5532114
This commit is contained in:
Rob Pike 2012-01-23 08:40:13 -08:00
parent fcfed1479e
commit 633a2ce096
1 changed files with 36 additions and 12 deletions
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48
doc/go_spec.html
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@ -1,6 +1,6 @@
<!--{
"Title": "The Go Programming Language Specification",
"Subtitle": "Version of January 13, 2012"
"Subtitle": "Version of January 21, 2012"
}-->
<!--
@ -2108,7 +2108,7 @@ Within a composite literal of array, slice, or map type <code>T</code>,
elements that are themselves composite literals may elide the respective
literal type if it is identical to the element type of <code>T</code>.
Similarly, elements that are addresses of composite literals may elide
the <code>&T</code> when the the element type is <code>*T</code>.
the <code>&amp;T</code> when the the element type is <code>*T</code>.
</p>
@ -2117,7 +2117,7 @@ the <code>&T</code> when the the element type is <code>*T</code>.
[...]Point{{1.5, -3.5}, {0, 0}} // same as [...]Point{Point{1.5, -3.5}, Point{0, 0}}
[][]int{{1, 2, 3}, {4, 5}} // same as [][]int{[]int{1, 2, 3}, []int{4, 5}}
[...]*Point{{1.5, -3.5}, {0, 0}} // same as [...]*Point{&Point{1.5, -3.5}, &Point{0, 0}}
[...]*Point{{1.5, -3.5}, {0, 0}} // same as [...]*Point{&amp;Point{1.5, -3.5}, &amp;Point{0, 0}}
</pre>
<p>
@ -2572,6 +2572,20 @@ var pt *Point
pt.Scale(3.5) // method call with receiver pt
</pre>
<p>
In a function call, the function value and arguments are evaluated in
<a href="#Order_of_evaluation">the usual order</a>.
After they are evaluated, the parameters of the call are passed by value to the function
and the called function begins execution.
The return parameters of the function are passed by value
back to the calling function when the function returns.
</p>
<p>
Calling a <code>nil</code> function value
causes a <a href="#Run_time_panics">run-time panic</a>.
</p>
<p>
As a special case, if the return parameters of a function or method
<code>g</code> are equal in number and individually
@ -3042,6 +3056,8 @@ As an exception to the addressability requirement, <code>x</code> may also be a
For an operand <code>x</code> of pointer type <code>*T</code>, the pointer
indirection <code>*x</code> denotes the value of type <code>T</code> pointed
to by <code>x</code>.
If <code>x</code> is <code>nil</code>, an attempt to evaluate <code>*x</code>
will cause a <a href="#Run_time_panics">run-time panic</a>.
</p>
<pre>
@ -4189,9 +4205,17 @@ GoStmt = "go" Expression .
</pre>
<p>
The expression must be a call, and
The expression must be a call.
The function value and parameters are
<a href="#Calls">evaluated as usual</a>
in the calling goroutine, but
unlike with a regular call, program execution does not wait
for the invoked function to complete.
Instead, the function begins executing independently
in a new goroutine.
When the function terminates, its goroutine also terminates.
If the function has any return values, they are discarded when the
function completes.
</p>
<pre>
@ -4359,8 +4383,6 @@ Regardless of how they are declared, all the result values are initialized to th
<p>
<span class="alert">
TODO: Define when return is required.<br />
TODO: Language about result parameters needs to go into a section on
function/method invocation<br />
</span>
</p>
-->
@ -4493,9 +4515,11 @@ DeferStmt = "defer" Expression .
<p>
The expression must be a function or method call.
Each time the "defer" statement
executes, the parameters to the function call are evaluated and saved anew but the
function is not invoked.
Deferred function calls are executed in LIFO order
executes, the function value and parameters to the call are
<a href="#Calls">evaluated as usual</a>
and saved anew but the
actual function is not invoked.
Instead, deferred calls are executed in LIFO order
immediately before the surrounding function returns,
after the return values, if any, have been evaluated, but before they
are returned to the caller. For instance, if the deferred function is
@ -4503,6 +4527,8 @@ a <a href="#Function_literals">function literal</a> and the surrounding
function has <a href="#Function_types">named result parameters</a> that
are in scope within the literal, the deferred function may access and modify
the result parameters before they are returned.
If the deferred function has any return values, they are discarded when
the function completes.
</p>
<pre>
@ -5355,9 +5381,7 @@ A struct or array type has size zero if it contains no fields (or elements, resp
</p>
<span class="alert">
<h2 id="Implementation_differences">Implementation differences - TODO</h2>
<ul>
<li><code>len(a)</code> is only a constant if <code>a</code> is a (qualified) identifier denoting an array or pointer to an array.</li>
<li><span class="alert"><code>len(x)</code> is only a constant if <code>x</code> is a (qualified) identifier denoting an array or pointer to an array.</span></li>
</ul>
</span>