Using Lambda Functions

What is this page about?

This page explains how to use lambda functions inside LINQ Reporting Engine templates.

LINQ Reporting Engine enables you to use lambda functions only as arguments of built-in enumeration extension methods in template expressions. See “Appendix A. Enumeration Extension Methods” for more information.

Note – Lambda functions declared within template expressions are not interchangeable with delegates. Thus, you can not pass delegates as arguments to built-in enumeration extension methods.

You can use both explicit and implicit lambda function signatures in template expressions. If you do not specify the type of a parameter of a lambda function explicitly, the type is determined implicitly by the engine depending on the type of the corresponding enumeration.

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FAQ

1. Q: Can I pass a regular delegate to a LINQ Reporting Engine enumeration method?
   A: No. Lambda functions used in template expressions are not interchangeable with delegates, and the engine does not accept delegate instances as arguments for its built‑in enumeration extension methods.

2. Q: Do I have to declare the parameter types explicitly in a lambda function inside a template?
   A: No. You may omit the parameter types; the engine will infer them automatically based on the type of the collection being enumerated. Explicit types can be used when you need to clarify the signature.

3. Q: Which enumeration extension methods support lambda functions?
   A: Only the built‑in enumeration extension methods listed in Appendix A. Enumeration Extension Methods (such as Where, Select, OrderBy, etc.) accept lambda functions as arguments. Custom methods are not supported.

4. Q: Are lambda functions allowed in other parts of a template, such as field expressions or conditional statements?
   A: Lambda functions are limited to arguments of the supported enumeration extension methods. They cannot be used directly in IF fields, MERGEFIELDs, or other non‑enumeration expressions.

5. Q: How do I write an implicit lambda function in a template expression?
   A: Use the syntax x => x.Property without specifying the type of x. The engine determines the type of x from the collection being processed, e.g., {{#foreach item in Employees.Where(e => e.IsActive)}}.