Setting a parameter's default value and validating datatype withattributes.

  • Thread starter Thread starter Jimmo
  • Start date Start date
J

Jimmo

I have written a parameter attribute class
("AttributeTargets.Parameter). One of several the constructor
arguments is a parameter to specify a default value for the method's
parameter.

I would like to emulate InteropServices.DefaultParameterValueAttribute
behavior where at compile time, the specified default value is
validated against the method's data type and results in a compilation
failure if the validation fails. I don't see:
a. How I can gain access to the method's parameter info (specifically
datatype) to perform the validation.
b. How the resultant failed validation causes the compiler to fail
with error.

Any suggestions? I prefer not to have to call
DefaultParameterValueAttribute in addition to my attribute class?
Alternatively, is there a way to hijack the
DefaultParameterValueAttribute behavior in my class to achieve the
same result?

Thanks,

- Jim
 
Jimmo,

You will have to do this ^after^ compile time. Currently, the compiler
doesn't have any hooks that allow you to do this sort of thing.

However, you can create a custom MSBUILD task which you place in your
project which will fail the build process.

In your task, you would simply reflect on all the methods on all the
types in the assembly output by the project. Since attributes don't know
what they are attached to, you have to take a look at the attributes applied
to all the methods to find where your attribute is applied, then perform the
check.
 
Jimmo,

    You will have to do this ^after^ compile time.  Currently, the compiler
doesn't have any hooks that allow you to do this sort of thing.

    However, you can create a custom MSBUILD task which you place in your
project which will fail the build process.

    In your task, you would simply reflect on all the methods on all the
types in the assembly output by the project.  Since attributes don't know
what they are attached to, you have to take a look at the attributes applied
to all the methods to find where your attribute is applied, then perform the
check.

--
          - Nicholas Paldino [.NET/C# MVP]
          - (e-mail address removed)




I have written a parameter attribute class
("AttributeTargets.Parameter).  One of several the constructor
arguments is a parameter to specify a default value for the method's
parameter.
Click to expand...
I would like to emulate InteropServices.DefaultParameterValueAttribute
behavior where at compile time, the specified default value is
validated against the method's data type and results in a compilation
failure if the validation fails.  I don't see:
a.  How I can gain access to the method's parameter info (specifically
datatype) to perform the validation.
b.  How the resultant failed validation causes the compiler to fail
with error.
Click to expand...
Any suggestions?  I prefer not to have to call
DefaultParameterValueAttribute in addition to my attribute class?
Alternatively, is there a way to hijack the
DefaultParameterValueAttribute behavior in my class to achieve the
same result?

- Jim- Hide quoted text -
Click to expand...

- Show quoted text -
Click to expand...

Hi Nicholas,

Not the answer I was hoping for, but the one I expected. I'll give
your approach a shot...

Thanks for responding....

- jim
 
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