Add section about extending Computation Expression Builders #5826
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@cartermp, can you take a look at this PR? |
mairaw
changed the title
mairaw
requested changes
Jul 10, 2018
| ## Custom Operations | ||
| You can define a custom operation on a computation expression and use a custom operation as an operator in a computation expression. For example, you can include a query operator in a query expression. When you define a custom operation, you must define the Yield and For methods in the computation expression. To define a custom operation, put it in a builder class for the computation expression, and then apply the [`CustomOperationAttribute`](https://msdn.microsoft.com/library/199f3927-79df-484b-ba66-85f58cc49b19). This attribute takes a string as an argument, which is the name to be used in a custom operation. This name comes into scope at the start of the opening curly brace of the computation expression. Therefore, you shouldn’t use identifiers that have the same name as a custom operation in this block. For example, avoid the use of identifiers such as `all` or `last` in query expressions. | ||
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| ### Extending existing Builders with new Custom Operatios |
| ### Extending existing Builders with new Custom Operatios | ||
| If you already have a builder class, its custom operations can be extended from outside of this builder class. Extensions must be declared in modules. Namespaces cannot contain extension members except in the same file and namespace declaration group where the type is defined. | ||
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| For instance extending the existing `Microsoft.FSharp.Linq.QueryBuilder` class. |
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It would probably be better to say something like:
"The following example shows how to extend an existing Microsoft.FSharp.Linq.QueryBuilder class:"
| You can define a custom operation on a computation expression and use a custom operation as an operator in a computation expression. For example, you can include a query operator in a query expression. When you define a custom operation, you must define the Yield and For methods in the computation expression. To define a custom operation, put it in a builder class for the computation expression, and then apply the [`CustomOperationAttribute`](https://msdn.microsoft.com/library/199f3927-79df-484b-ba66-85f58cc49b19). This attribute takes a string as an argument, which is the name to be used in a custom operation. This name comes into scope at the start of the opening curly brace of the computation expression. Therefore, you shouldn’t use identifiers that have the same name as a custom operation in this block. For example, avoid the use of identifiers such as `all` or `last` in query expressions. | ||
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| ### Extending existing Builders with new Custom Operatios | ||
| If you already have a builder class, its custom operations can be extended from outside of this builder class. Extensions must be declared in modules. Namespaces cannot contain extension members except in the same file and namespace declaration group where the type is defined. |
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adding the word same in front of namespace declaration group would probably make it easier to understand
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Sure! |
mairaw
approved these changes
Jul 13, 2018
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It is not much text, but I hope it conveys the concept. For the example I was looking at existing builders and an easy, understandable example.
Fixes #5769