MATCHER*() should allow specifying negative description

[GoogleCodeExporter]

The MATCHER() and MATCHER_Pn() macros are convenient for creating new
matchers.  They are much simpler to use than implementing
MatcherInterface directly.  However, there's one thing that prevents a
matcher defined using MATCHER*() to be library-quality: the
description of the negation of the matcher doesn't look so nice.

For example, given:

 MATCHER(IsEven, "") { return (arg % 2) == 0; }

the assertion

 EXPECT_THAT(x, IsEven());

can print a message like:

 Value of: x
 Expected: is even
   Actual: 5

which is good.  However,

 EXPECT_THAT(x, Not(IsEven()));

can print something like:

 Value of: x
 Expected: not (is even)
   Actual: 6

The "not (is even)" message isn't as good as a custom-defined matcher
can generate ("is not even" or perhaps "is odd").

It will be a lot of hassle to implement MatcherInterface just so that
we can get a better negative description message.  Therefore I propose
to extend the MATCHER* format string to allow (optionally) specifying
the negative description.  One possible scheme is to use "%-" as the
divider for the positive and the negative descriptions:

 MATCHER(IsEven, "is even%-is not even") { ... }

If either side of "%-" is empty, the default description will be used.
Therefore the above is equivalent to:

 MATCHER(IsEven, "%-is not even") { ... }

(Note that we already reserve "%" as a meta character in MATCHER*'s
format spec string.)

Original issue reported on code.google.com by zhanyong...@gmail.com on 24 Aug 2009 at 6:13

[GoogleCodeExporter]

Working on it right now with a different design.

Original comment by w...@google.com on 5 Jun 2010 at 6:43

• Changed state: Started
• Added labels: Priority-High
• Removed labels: Priority-Low

[GoogleCodeExporter]

Original comment by w...@google.com on 22 Jul 2010 at 4:47

• Changed state: Fixed