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Added static warning on assignment to final locals; adjusted for-in.

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Addresses spec omission which was brought up in SDK issue #30483.

The following issue was created specifically on this topic: #30489.

R=lrn@google.com

Review-Url: https://codereview.chromium.org/2998073002 .
This commit is contained in:
Erik Ernst 2017-08-21 09:29:15 +02:00
parent 3cac905c54
commit 6ef388db9d
1 changed files with 23 additions and 6 deletions
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29
docs/language/dartLangSpec.tex
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@ -22,6 +22,7 @@
% 2.0
% - Don't allow functions as assert test values.
% - Start running "async" functions synchronously.
% - It is a static warning and dynamic error to assign to a final local.
%
% 1.15
% - Change how language specification describes control flow.
@ -449,6 +450,7 @@ A {\em final variable} is a variable whose binding is fixed upon initialization;
It is a static warning if a final instance variable that has been initialized at its point of declaration is also initialized in a constructor.
% It is a static warning if a final instance variable that has been initialized by means of an initializing formal of a constructor is also initialized elsewhere in the same constructor.
It is a compile-time error if a local variable $v$ is final and $v$ is not initialized at its point of declaration.
It is a static warning and a dynamic error to assign to a final local variable.
\commentary{
@ -5953,16 +5955,26 @@ It is a static warning if the static type of $c$ may not be assigned to \cd{bool
\LMLabel{for-in}
\LMHash{}
A for statement of the form \code{ \FOR{} ($finalConstVarOrType?$ id \IN{} $e$) $s$} is equivalent to the following code:
Let $D$ be derived from \code{finalConstVarOrType?}
and let $n0$ be an identifier that does not occur anywhere in the program.
A for statement of the form \code{\FOR{} ($D$ $id$ \IN{} $e$) $s$} is equivalent to the following code:
\begin{dartCode}
var n0 = $e$.iterator;
\WHILE{} (n0.moveNext()) \{
$finalConstVarOrType?$ id = n0.current;
\VAR{} $n0$ = $e$.iterator;
\WHILE{} ($n0$.moveNext()) \{
$D$ $id$ = $n0$.current;
$s$
\}
\end{dartCode}
where \code{n0} is an identifier that does not occur anywhere in the program, except that for purposes of static typechecking, it is checked under the assumption that $n0$ is declared to be of type $T$, where $T$ is the static type of $e.iterator$.
For purposes of static typechecking,
this code is checked under the assumption that $n0$ is declared to be of type $T$,
where $T$ is the static type of \code{$e$.iterator}.
\commentary{
It follows that it is a static warning if $D$ is empty and $id$ is a final variable,
and a dynamic error will then occur if the body is executed.
}
\subsubsection{Asynchronous For-in}
\LMLabel{asynchronousFor-in}
@ -5971,11 +5983,16 @@ where \code{n0} is an identifier that does not occur anywhere in the program, ex
A for-in statement may be asynchronous. The asynchronous form is designed to iterate over streams. An asynchronous for loop is distinguished by the keyword \AWAIT{} immediately preceding the keyword \FOR.
\LMHash{}
Execution of a for-in statement, $f$, of the form \code{\AWAIT{} \FOR{} (finalConstVarOrType? $id$ \IN{} $e$) $s$} proceeds as follows:
Let $D$ be derived from \code{finalConstVarOrType?}.
Execution of a for-in statement, $f$, of the form
\code{\AWAIT{} \FOR{} ($D$ $id$ \IN{} $e$) $s$}
proceeds as follows:
\LMHash{}
The expression $e$ is evaluated to an object $o$.
It is a dynamic error if $o$ is not an instance of a class that implements \code{Stream}.
It is a static warning if $D$ is empty and $id$ is a final variable,
and it is then a dynamic error if the body is executed.
\LMHash{}
The stream associated with the innermost enclosing asynchronous for loop, if any, is paused.