ParameterInfo properties, attributes and out ref parameters of the methods

引用: http://stackoverflow.com/questions/15636969/parameterinfo-properties-attributes-and-out-ref-parameters-of-the-methods

Well, I'm confused by the properties of the ParameterInfo class.
Unfortunately documentation is not very clear: examples show how to build methods but don't show how these methods look in C#.

Cane somebody tell more about these properties:

• DefaultValue
• HasDefaultValue
• IsIn
• IsLcid
• IsOptional
• IsOut
• IsRetval

And which combination leads to what method params.
I made a simple program which gives the following output:

Method name M1 void M1(object param)
IL signature: .method public hidebysig instance void M1(object param) cil managed
Method parameter description:
Is passed by reference False
HasDefaultValue=False
IsIn=False
IsLcid=False
IsOptional=False
IsOut=False
IsRetVal=False

Method name M2 void M2(object param = null)
IL signature .method public hidebysig instance void M2([opt] object param) cil managed
Method parameter description:
Is passed by reference False
HasDefaultValue=True
DefaultValue=null
IsIn=False
IsLcid=False
IsOptional=True
IsOut=False
IsRetVal=False

Method name M3 void M3(out object param)
IL signature .method public hidebysig instance void M3([out] object& param) cil managed
Method parameter description:
Is passed by reference True
HasDefaultValue=False
IsIn=False
IsLcid=False
IsOptional=False
IsOut=True
IsRetVal=False

Method name M4 void M4(ref object param)
IL signature .method public hidebysig instance void M4(object& param) cil managed
Method parameter description:
Is passed by reference True
HasDefaultValue=False
IsIn=False
IsLcid=False
IsOptional=False
IsOut=False
IsRetVal=False

Method name M5 void M5([In] object param)
IL signature .method public hidebysig instance void M5([in] object param) cil managed
Method parameter description:
Is passed by reference False
HasDefaultValue=False
IsIn=True
IsLcid=False
IsOptional=False
IsOut=False
IsRetVal=False

Method name M6 void M6([Out] object param)
IL signature .method public hidebysig instance void M6([out] object param) cil managed
Method parameter description:
Is passed by reference False
HasDefaultValue=False
IsIn=False
IsLcid=False
IsOptional=False
IsOut=True
IsRetVal=False

Method name M7 void M7([Out] out object param)
IL signature .method public hidebysig instance void M7([out] object& param) cil managed
Method parameter description:
Is passed by reference True
HasDefaultValue=False
IsIn=False
IsLcid=False
IsOptional=False
IsOut=True
IsRetVal=False

Method name M8 void M8([DefaultValue(null)] object param)
IL signature .method public hidebysig instance void M8(object param) cil managed
Method parameter description:
Is passed by reference False
HasDefaultValue=False
IsIn=False
IsLcid=False
IsOptional=False
IsOut=False
IsRetVal=False

Method name M9 void M9([DefaultValue(-10)] int param = 10)
IL signature .method public hidebysig instance void M9([opt] int32 param) cil managed
Method parameter description:
Parameter name param
Is passed by reference False
HasDefaultValue=True
DefaultValue=10
IsIn=False
IsLcid=False
IsOptional=True
IsOut=False
IsRetVal=False

Method name M10 void M10([Optional] int param)
IL signature .method public hidebysig instance void M10([opt] int32 param) cil managed
Method parameter description:
Is passed by reference False
HasDefaultValue=False
IsIn=False
IsLcid=False
IsOptional=True
IsOut=False
IsRetVal=False

I guess In, Out and Optional attributes relate to COM as they are located in System.Runtime.InteropServices namesapce.
But again documentation is quite poor. 🙁

And what is RetVal and where it is used?