'|' is part of the character set for operators, but within the
signature of a closure we need to treat the first non-nested '|' as
the closing delimiter for the closure parameter list. For example,
{ |x = 1| 2 + x}
parses with the default value of '1' for x, with the body 2 + x. If
the '|' operator is needed in the default value, it can be wrapped in
parentheses:
{ |x = (1|2)| x }
Note that we have problems with both name binding and type checking
for default values in closures (<rdar://problem/13372694>), so they
aren't actually enabled. However, this allows us to parse them and
recover better in their presence.
Swift SVN r5202
This commit implements closure syntax that places the (optional)
parameter list in pipes within the curly braces of a closure. This
syntax "slides" well from very simple closures with anonymous
arguments, e.g.,
sort(array, {$1 > $0})
to naming the arguments
sort(array, {|x, y| x > y})
to adding a return type and/or parameter types
sort(array, {|x : String, y : String| -> Bool x > y})
and with multiple statements in the body:
sort(array, {|x, y|
print("Comparing \(x) and \(y)\n")
return x > y
})
When the body contains only a single expression, that expression
participates in type inference with its enclosing expression, which
allows one to type-check, e.g.,
map(strings, {|x| x.toUpper()})
without context. If one has multiple statements, however, one will
need to provide additional type information either with context
strings = map(strings, {
return $0.toUpper()
})
or via annotations
map(strings, {|x| -> String
return x.toUpper()
}
because we don't perform inter-statement type inference.
The new closure expressions are only available with the new type
checker, where they completely displace the existing { $0 + $1 }
anonymous closures. 'func' expressions remain unchanged.
The tiny test changes (in SIL output and the constraint-checker test)
are due to the PipeClosureExpr AST storing anonymous closure arguments
($0, $1, etc.) within a pattern in the AST. It's far cleaner to
implement this way.
The testing here is still fairly light. In particular, we need better
testing of parser recovery, name lookup for closures with local types,
more deduction scenarios, and multi-statement closures (which don't
get exercised beyond the unit tests).
Swift SVN r5169
