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Type Coercion is the conversion of one type of object to a new object of a different type with similar content. Tapestry frequently must coerce objects from one type to another. A common example is the coercion of a string into an integer or a double.

See Type Coercer Service for the list of build-in coercions.

Parameter Type Coercions

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Content by Label showLabels false showSpace false title Related Articles cql label in ("coercion","parameters") and space = currentSpace() } {info:title=Related Articles} * [TypeCoercer Service|IoC - coerce] {info} {float}

Tapestry automatically handles type coercions for component parameters.

Type coercions occur when a value passed into a parameter (as bound in a template or in an annotation) does not match the type of the parameter.For example, consider the Count component:

Code Block
java language java
public class Count { @Parameter private int start = 1; @Parameter(required = true) private int end; @Parameter private int value; . . .

 

Here, the type of all three parameters is int.

However, it is likely that the component will be used as so:

Code Block
java language java
Merry Christmas: <t:count end="3"> Ho! </t:count>

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Tapestry will automatically coerce the bound value, a long, to the parameter's type, int. This may be a lossy coercion (if the long represents a number larger than can be stored in an int).

TypeCoercer Service

Main Article: TypeCoercer Service Type Coercion

The TypeCoercer service is responsible for this type coercion. This service is part of the tapestry-ioc module. The service is quite extensible, allowing for new types and coercions to be added easily. The TapestryModule contributes a few additional coercions into the TypeCoercer service.