| ---- | |
| Parameter Type Coercions | |
| ---- | |
| Parameter Type Coercions | |
| Tapestry automatically handles type coercions for parameters. | |
| Type coercions occur when a value passed into a parameter (as bound in template or | |
| in an annoation) does not match the type of the parameter. | |
| For example, consider the Count component: | |
| +---+ | |
| 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: | |
| +---+ | |
| Merry Christmas: <t:count end="3"> Ho! </t:count> | |
| +---+ | |
| A bare whole number is interpreted by the prop binding prefix as a long. So this is the <long> value 3. | |
| 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 | |
| The TypeCoercer service is responsible for this type coercion. This service is part of the tapestry-ioc module, and | |
| is {{{../../tapestry-ioc/coerce.html}documented there}}. 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. | |