Named parameter are not working in this code can anyone help me with this .I took this code from geeksofgeeks

[Baldev Singh]

void gfg1(int g1, [ int g2 ])
{
    // Creating function 1
    print("g1 is $g1");
    print("g2 is $g2");
}

void gfg2(int g1, { int g2, int g3 })
{
    // Creating function 1
    print("g1 is $g1");
    print("g2 is $g2");
    print("g3 is $g3");
}

void gfg3(int g1, { int g2 : 12 })
{
    // Creating function 1
    print("g1 is $g1");
    print("g2 is $g2");
}

void main()
{
    // Calling the function with optional parameter
    print("Calling the function with optional parameter:");
    gfg1(01);

    // Calling the function with Optional Named parameter
    print("Calling the function with Optional Named parameter:");
    gfg2(01, g3 : 12);

    // Calling function with default valued parameter
    print("Calling function with default valued parameter");
    gfg3(01);
}

Error:

lib/main.dart:2:25: Error: The parameter 'g2' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'. void gfg1(int g1, [ int g2 ]) ^^ lib/main.dart:9:25: Error: The parameter 'g2' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'. void gfg2(int g1, { int g2, int g3 }) ^^ lib/main.dart:9:33: Error: The parameter 'g3' can't have a value of 'null' because of its type 'int', but the implicit default value is 'null'. void gfg2(int g1, { int g2, int g3 }) ^^ Error: Compilation failed.

[Brett Sutton]

Looks like the code was written pre NNBD.

change 

void gfg1(int g1, [ int g2 ])

to 

void gfg1(int g1, [ int? g2 ])

The same for any other optional parameters unless you provide a default value.

S. Brett Sutton

Noojee Contact Solutions

03 8320 8100

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[Shlomo Belleli]

Here is your code running just fine in DartPad

you missed the "?" operator for the  null safety

here 

  void gfg1(int g1, [ int? g2 ])

and here

  void gfg2(int g1, { int? g2, int? g3 })

void gfg1(int g1, [ int? g2 ])

{
    // Creating function 1
    print("g1 is $g1");
    print("g2 is $g2");
}

void gfg2(int g1, { int? g2, int? g3 })

{
    // Creating function 1
    print("g1 is $g1");
    print("g2 is $g2");
    print("g3 is $g3");
}

void gfg3(int g1, { int g2 : 12 })
{
    // Creating function 1
    print("g1 is $g1");
    print("g2 is $g2");
}

void main()
{
    // Calling the function with optional parameter
    print("Calling the function with optional parameter:");
    gfg1(01);

    // Calling the function with Optional Named parameter
    print("Calling the function with Optional Named parameter:");
    gfg2(01, g3 : 12);

    // Calling function with default valued parameter
    print("Calling function with default valued parameter");
    gfg3(01);
}