Quoting Eliot Miranda <eliot.miranda@gmail.com>:

Hi Phillipe,

On Mon, May 26, 2014 at 12:51 AM, Philippe Marschall <philippe.marschall@netcetera.ch> wrote:

Hi

I have been investigating why Dictionary look up performance with String keys is not as good as I would expected. Something I noted is that String >> #= is implemented in terms of #compare:with:collated:. There is no short circuit if Strings are not the same size. In my case some Strings have the same prefix but a different length eg 'Content-Type' and 'Content-Length'. In that case a #compare:with:collated: is performed even though we know in advance the answer will be false because they have different sizes.

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Why not rewrite

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String>>= aString��

"Answer whether the receiver sorts equally as aString.

The collation order is simple ascii (with case differences)."

aString isString ifFalse: [ ^ false ].

^ (self compare: self with: aString collated: AsciiOrder) = 2

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as

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String>>= aString��

"Answer whether the receiver sorts equally as aString.

The collation order is simple ascii (with case differences)."

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(aString isString

and: [self size = aString size]) ifFalse: [^false].

^ (self compare: self withSize: with: aString collated: AsciiOrder) = 2

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?

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One /could/ add a replacement compare:with:collated: primitive��primitiveCompareString which took the sizes as arguments to avoid asking twice. ��But it wouldn't be safe. ��One could abuse the primitive and lie about the size. ��So I suspect it is best to add the size check to String>>#= and accept the duplication of the��primitive��finding the sizes of the two strings. ��The cost in the primitive is minimal. ��A WideString version of the primitive might pay its way, but if Spur and Sista arrive soon the primitive shouldn't be faster than the optimised Smalltalk code.
--
best,

Eliot

BTW, any good reason for not prefixing all the implementors of #= with this?

"Any object is equal to itself"
self == argument ifTrue: [ ^ true ].