xslt是/when选择比if更有效-xsltis/whenischoosemoreefficientthanif

2  

When I looked into this ages ago, the only guidance I could find was in this KB article:

当我在很久以前看过这篇文章时,我能找到的唯一指导就是这篇知识库文章:

INFO: Techniques to Improve Performance of XSL Transformations

信息:提高XSL转换性能的技术

Reduce the usage of xsl:choose/xsl:when/xsl:otherwise. Performance is effected [sic] when the majority of selections fall through the otherwise clause. Therefore, match with when, and try to avoid using otherwise when you know that a particular value exists.

减少xsl的使用:select / xsl:when / xsl:否则。当大多数选择通过其他条款落实时,性能[sic]实现。因此,当您知道特定值存在时,请与when匹配,并尽量避免使用。

But I'm guessing it would be dependant on the XSLT processor you're using.

但我猜它会依赖于你正在使用的XSLT处理器。

3  

In this instance it wouldn't actually make much difference. Your second 'when' test is only being executed one less time than your first.

在这种情况下,实际上并没有太大的区别。你的第二次“何时”测试只比你的第一次执行时间短。

That said, I would use the choose/when/otherwise solution if you are never expecting nor wanting both of these conditions to be true. It wouldn't seem logical to test both conditions knowing only one will be true, but depending on the factors being tested this will be inevitable.

也就是说,如果您从未期望也不希望这两个条件都成立,我会使用choose / when / otherwise解决方案。知道只有一个条件是真的,测试这两个条件似乎不合逻辑,但根据被测试的因素,这将是不可避免的。

Of course the benefit of the 'choose' is that you can easily set a fallback option, but you are not taking advantage of this. Not that it will make much difference but this 'otherwise' line will be executed whenever the two conditions return false even though it contains nothing.

当然,“选择”的好处是您可以轻松设置后备选项,但您没有利用这一点。并不是说它会有很大的不同,但只要两个条件返回false就会执行这个“其他”行,即使它什么都不包含。

If you were doing this conditional statement in another language like Javascript you probably wouldn't think twice about using if/else if/else solution - again, because you only want one condition to ever be true.

如果您使用其他语言(如Javascript)执行此条件语句,您可能不会再考虑使用if / else if / else解决方案 - 再次,因为您只希望一个条件永远为真。

I'm afraid the use of 'choose' over 'if' is conditional, it all depends on the data you are processing and what you are testing.

我担心使用'select'而不是'if'是有条件的,这完全取决于你正在处理的数据和你正在测试的内容。

This might be useful to an extent, another dev's view: http://xsltbyexample.blogspot.com/2008/02/when-to-use-xslif-and-xslwhen.html

这可能在某种程度上是有用的,另一个开发者的观点:http://xsltbyexample.blogspot.com/2008/02/when-to-use-xslif-and-xslwhen.html

1  

It probably makes no significant difference, but in the version with the two if tests, both of the XPath conditions are always executed, whereas in the choose case, if the first if matches, the second will never have to be executed.

它可能没有显着区别,但在具有两个if测试的版本中,两个XPath条件总是被执行,而在选择情况下,如果第一个if匹配,则第二个将永远不必执行。

Stylus Studio, Oxygen, etc. all have profilers which measure this sort of thing, because like most optimization, it's usually best to measure and actually see than to try to do it by feel. And the particular XSLT engine will make a huge difference here.

Stylus Studio,Oxygen等都有测量这种东西的分析器,因为像大多数优化一样,通常最好测量并实际看到,而不是尝试通过感觉来做。特定的XSLT引擎将在这里产生巨大的变化。

1  

It's very unlikely to make a difference. If it does, the difference will depend entirely on what XSLT processor you are using. The answer to performance questions is always: "measure it!".

它不太可能有所作为。如果是这样,差异将完全取决于您使用的XSLT处理器。性能问题的答案总是:“衡量它!”。