languages/dart-sdk
languages/dart-sdk
1
0
Fork 0
mirror of https://github.com/dart-lang/sdk synced 2024-10-14 09:12:08 +00:00
Code Issues Packages Projects Releases Wiki Activity

Disallow expressions statements starting with {.

Browse source 
The current specification only prohibits expressions statements where the
expression *is* a map, not those that *start with* a map.
Implementations have always rejected those starting with a map.

Bug: http://dartbug.com/725
Change-Id: I805a6f82d1afdcf335aff73e74dac1f14e5a6afe
Reviewed-on: https://dart-review.googlesource.com/71247
Commit-Queue: Lasse R.H. Nielsen <lrn@google.com>
Reviewed-by: Erik Ernst <eernst@google.com>
This commit is contained in:
Lasse Reichstein Holst Nielsen 2018-08-27 12:43:56 +00:00 committed by commit-bot@chromium.org
parent 8b92fe3bbd
commit f6242cb100
1 changed files with 20 additions and 8 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

28
docs/language/dartLangSpec.tex
View file

@ -25,6 +25,8 @@
% constructor invocation.
% - Specify that type arguments passed in a redirecting factory constructor
% declaration must be taken into account during static checks.
% - Disallow any expression statement starting with `{`, not just
% those that are map literals.
%
% 2.0
% - Don't allow functions as assert test values.
@ -7826,11 +7828,8 @@ A block statement introduces a new scope, which is nested in the lexically enclo
\LMLabel{expressionStatements}
\LMHash{}
An {\em expression statement} consists of an expression other than a non-constant map literal (\ref{maps}) that has no explicit type arguments.
\rationale{
The restriction on maps is designed to resolve an ambiguity in the grammar, when a statement begins with \{.
}
An {\em expression statement} consists of an expression that does not
begin with a \{ character.
\begin{grammar}
{\bf expressionStatement:}expression? `{\escapegrammar ;}'
@ -7838,11 +7837,24 @@ The restriction on maps is designed to resolve an ambiguity in the grammar, when
\end{grammar}
\LMHash{}
Execution of an expression statement \code{$e$;} proceeds by evaluating $e$.
The expression of an expression statement is not allowed to begin with a \{.
\commentary{
This means that if some source text could otherwise be parsed as an expression
followed by a \;, then this grammar production does not apply
when the expression starts with a \{.
}
\rationale{
The restriction resolves an ambiguity while parsing where a
\{ can start either a block (\ref{blocks}) or a map literal (\ref{maps}).
By disallowing the latter from starting an expression statement,
the parser does not need to look further ahead
before deciding that it is parsing a block statement.
}
\LMHash{}
It is a compile-time error if a non-constant map literal that has no explicit type arguments appears in a place where a statement is expected.
Execution of an expression statement \code{$e$;} proceeds by evaluating $e$.
If the expression evaluates to a value, then the value is ignored
and the execution completes normally.
\subsection{Local Variable Declaration}
\LMLabel{localVariableDeclaration}