Shared ambiguity instance

[nieqiurong]

When a conflicting key is encountered when generating a short key, we can share an instance to reduce memory usage.

[coveralls]

coverage: 87.174% (-0.003%) from 87.177%
when pulling 4a9d42c on nieqiurong:shared-ambiguity
into b5236ec on mybatis:master.

[harawata]

Thank you for the PR, @nieqiurong ,

I could be wrong, but this seems to make the error message less informative.
Please add a test case.

[harawata]

Ah, I see, you are now using key instead of .getSubject().
In that case, we should remove subject from Ambiguity, or am I still missing something?

[epochcoder]

imo, if we are going to throw an exception when an ambiguous key is detected, we might as well remove the inner class entirely and do that where it is detected, as essentially this just makes it a kind of a maker interface and getSubject() useless, but agree that there definitely needs to be a test case for this.

[nieqiurong]

Yes, because the key is originally the value that was put in. When the key value is repeated, we can use a fixed value as the value, which can be a specific Object.

[nieqiurong]

I'll modify it later.

[harawata]

I think we can remove Ambiguity immediately.
It's clearly internal.