问题:

Given an XSL 'If' statement:

<xsl:if test="a = 'some value' and b = 'another value'">

If a does not equal 'some value', is the value of b still checked? (As if the first test is false, the only outcome of the and is false.) This is what languages like C# do - I was wondering if the same goes in XSL. Does it depend on the engine/parser?

回答1:

Yes, it is called lazy-evaluation or short-circuiting, and xsl supports it. See: http://www.w3.org/TR/xpath#booleans

An and expression is evaluated by evaluating each operand and converting its value to a boolean as if by a call to the boolean function. The result is true if both values are true and false otherwise. The right operand is not evaluated if the left operand evaluates to false.

回答2:

Yes, this is depending on the implementation. But since XSLT is side-effect-free (as opposed to C# and other languages, where a function call chainging some state or even an assignment can be in the expression), this does not matter.