saxon:assign

The saxon:assign instruction is used to change the value of a global variable that has previously been declared using xsl:variable (or xsl:param). The variable or parameter must be marked as assignable by including the extra attribute saxon:assignable with value yes.

Category: instruction
Content: sequence-constructor
Permitted parent elements: any XSLT element whose content model is sequence-constructor; any literal result element

Attributes

name

eqname

The name of the variable

select?

expression

The new value may be given either by an expression in the select attribute, or by expanding the content of the saxon:assign element

Details

This instruction works only with global variables. It should be regarded as deprecated, and may be withdrawn completely at some time in the future, since it is incompatible with many of the optimizations that Saxon now performs.

There are better ways of achieving the same effect. Consider constructs such as tunnel parameters, xsl:iterate, higher-order functions, or xsl:accumulator.

If saxon:assign is used then multithreading should be disabled by setting the configuration property ALLOW_MULTITHREADING to false. A compile-time warning is issued if multi-threading is allowed, since the order of execution of instructions in the stylesheet is then unpredictable.

The new value is converted to the declared type of the variable using the function conversion rules. This may result in a type error if conversion is not possible.

The saxon:assign element itself does not allow an as attribute. Instead, it calculates the value of the variable as if as="item()*" were specified. This means that the result of the construct:

<saxon:assign name="a">London</saxon:assign>

is a single text node, not a document node containing a text node. If you want to create a document node, use xsl:document.

Note: Using saxon:assign is cheating. XSLT is designed as a language that is free of side-effects, which is why variables are not assignable. Once assignment to variables is allowed, certain optimizations become impossible. There are some circumstances in which the order of execution may not be quite what you expect, in which case saxon:assign may show anomalous behavior. In particular, avoid calling saxon:assign while evaluating variables, or from within a function called from a context such as a predicate. In principle the saxon:assignable attribute is designed to stop Saxon doing optimizations that cause such anomalies, but you can't always rely on this.

Saxon issues a warning if saxon:assign is used in a configuration that allows multi-threading, since the construct is not thread-safe. Multi-threading can be disabled using the configuration property ALLOW_MULTITHREADING.

The saxon:assign instruction can be exported to a SEF file; the resulting SEF file can be used by Saxon/J but not by Saxon-JS.

Examples

<xsl:variable name="i" select="0" saxon:assignable="yes"/> <xsl:template name="loop"> <saxon:while test="$i &lt; 10"> The value of i is <xsl:value-of select="$i"/> <saxon:assign name="i" select="$i+1"/> </saxon:while> </xsl:template>

See also

saxon:assignable

xsl:variable

xsl:param