<div dir="ltr">Hi Phillipe,<br><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, May 26, 2014 at 12:51 AM, Philippe Marschall <span dir="ltr"><<a href="mailto:philippe.marschall@netcetera.ch" target="_blank">philippe.marschall@netcetera.ch</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">Hi<br>
<br>
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.<br>
</blockquote><div><br></div><div>Why not rewrite</div><div><br></div><div>String>>= aString </div><div><span class="" style="white-space:pre"> </span>"Answer whether the receiver sorts equally as aString.</div>
<div><span class="" style="white-space:pre"> </span>The collation order is simple ascii (with case differences)."</div><div><span class="" style="white-space:pre"> </span></div><div><span class="" style="white-space:pre"> </span>aString isString ifFalse: [ ^ false ].</div>
<div><span class="" style="white-space:pre"> </span>^ (self compare: self with: aString collated: AsciiOrder) = 2</div><div><br></div><div>as</div><div><br></div><div><div>String>>= aString </div><div><span class="" style="white-space:pre"> </span>"Answer whether the receiver sorts equally as aString.</div>
<div><span class="" style="white-space:pre"> </span>The collation order is simple ascii (with case differences)."</div><div><br></div><div><span style="white-space:pre"> (</span>aString isString</div><div><span style="white-space:pre"> and: [self size = aString size]) i</span>fFalse: [^false].<br>
</div><div><span class="" style="white-space:pre"> </span>^ (self compare: self withSize: with: aString collated: AsciiOrder) = 2</div></div><div><br></div><div>?</div><div></div></div><div class="gmail_extra"><br></div>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.<br>
-- <br>best,<div>Eliot</div>
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