Emit metadata for auto-property initializers

[dsaf]

I want to be able to know what are the default values of properties without having to refer to documentation similarly to how optional method arguments work.
Would it be possible to emit reflectable metadata for property initializers?
This would be beneficial for auto-generated documentation and IDE hints.

At the moment my choices are:

public string Name { get; set; } = "John";

• + language idiomatic;
• + guaranteed to execute;
• + all values are supported;
• - black box - not introspectable/reflectable without instantiation;
• - documentation that is not generated from code is guaranteed to become out of sync;
• - no IDE hints.

[DefaultValue("John")]
public string Name { get; set; }

• - requires custom code;
• - not guaranteed to execute;
• - needs a version of attribute per type without a proper literal (e.g. DateTimeDefaultValue);
• + reflectable;
• + documentation is possible to generate from code;
• + IDE hints are possible with custom code.

Related SO question:

http://stackoverflow.com/questions/33383991/c-sharp-6-0-and-reflection-getting-value-of-property-initializers

[dsaf]

Of course optional method arguments have the following limitation:

A default value must be one of the following types of expressions:

• a constant expression;
• an expression of the form new ValType(), where ValType is a value type, such as an enum or a struct;
• an expression of the form default(ValType), where ValType is a value type.

https://msdn.microsoft.com/en-us/library/dd264739.aspx

[DavidArno]

I want to be able to know what are the default values of properties without having to refer to documentation similarly to how optional method arguments work.

The obvious solution would be "look at the code". I'm guessing that isn't an option for you though?

[dsaf]

@DavidArno It's a solution.

However it has a number of usability problems:

1. requires mentally parsing unrelated code;
2. requires active navigation as opposed to prompting a tooltip;
3. requires code availability or decompilation;
4. doesn't give a possibility of code hints, e.g. "You are setting this property to what is already it's default value within an object initializer, are you sure this is what you want to do?".

[svick]

all values are supported

I think this would be a significant problem. How do you represent arbitrary expressions/values in metadata?

[dsaf]

@svick Yes, I am afraid it might be a substantial problem.

[dsaf]

Somewhat related to #711.