Call .NET Methods with Optional Arguments

MATLAB^® supports calling .NET methods with optional arguments. In the MATLAB method signature, optional arguments are displayed using the optional<T> syntax, where T is a specific type.

To use a default method argument, pass an instance of System.Reflection.Missing.Value.

Call Nonoverloaded .NET Method

If a .NET method is not overloaded, you do not need to specify all optional arguments at the end of the parameter list. Omitted arguments use their default values. To run this example, build and load the NetDocOptional assembly from the C# source code using the directions in Build and Load .NET Assembly for MATLAB.

C# Method

The str1 and str2 parameters in this method are optional.

public string Greeting(int x,string str1="hello",string str2="world")

Call Method from MATLAB

First, display the Greeting method signature.

methodsview("netdoc.NetDocOptional")

Return Type	Name	Arguments
System.String RetVal	Greeting	(NetDocOptional.MyClass this, int32 scalar x, optional<System.String> str1, optional<System.String> str2)

From within MATLAB, call the Greeting method without the optional arguments. The returned string shows the default values of the optional arguments.

mlClass = NetDocOptional.MyClass;
Greeting(mlClass,0)

ans = 
hello world

Next, call the Greeting method using the default value for the first optional argument and a specified value for the second optional argument.

def = System.Reflection.Missing.Value;
Greeting(mlClass,0,def,"Mr. Jones")

ans = 
hello Mr. Jones

Finally, call the Greeting method using a specified value for the first optional argument and the default value for the second optional argument. In this case, you can omit the last argument.

Greeting(mlClass,0,"My")

ans = 
My world

NetDocOptional C# Source Code

This C# code defines the NetDocOptional.MyClass class, which includes the Greeting method with two optional string arguments.

using System;
using System.Text;

namespace NetDocOptional
{
    public class MyClass
    {
        public string Greeting(
            int x,
            string str1 = "hello",
            string str2 = "world")
        {
            return str1 + " " + str2;
        }
    }
}

Call Overloaded Method with Optional Arguments

If a .NET class has overloaded methods with optional arguments, MATLAB matches the method based on the number and type of provided input arguments.

• If the overloaded methods differ by the type, number, or dimension of their optional arguments, MATLAB first compares the types of mandatory arguments.

• If the mandatory argument types are different, MATLAB chooses the first overloaded method defined in the class.

• If the mandatory argument types are the same, you must specify enough optional arguments to make the method call unambiguous. Otherwise, MATLAB throws an error.

Call Method from MATLAB

Build your own .NET assembly Doc that defines the calc method in Class and load it into MATLAB.

Display the calc method signatures.

methodsview("netdoc.NetDocOptional")

Return Type	Name	Arguments
single scalar RetVal	calc	(Doc.Class this, optional<int32 scalar> x, optional<single scalar> y)
double scalar RetVal	calc	(Doc.Class this, optional<int32 scalar> x, optional<double scalar> y)

Usage in MATLAB

Create a Class object and then call calc with explicit arguments.

mlClass = Doc.Class;
calc(mlClass,3,4)

ans =
     7

If you try to use the default values by omitting the arguments, MATLAB cannot determine which signature to use.

calc(mlClass)

Cannot choose between the following .NET method signatures due to 
unspecified optional arguments in the call to 'calc':

'Doc.Class.calc(Doc.Class this, 
optional<int32 scalar> x, optional<single scalar> y)' and
'Doc.Class.calc(Doc.Class this, 
optional<int32 scalar> x, optional<double scalar> y)'

You can resolve this ambiguity by specifying enough additional 
optional arguments so that there is only one possible matching 
.NET method.

Resolve the ambiguity by specifying enough arguments or by passing System.Reflection.Missing.Value.

def = System.Reflection.Missing.Value;
calc(mlClass,def,def)
calc(mlClass,3,def)
calc(mlClass,def,4)

ans =
    44
ans =
    14
ans =
    37