Overload resolution with integer parameters for default literal

[ufcpp]

Recently, I found the following behavior:

X.M(0);       // M(int) 
X.M(default); // M(byte)

X.N(0);       // N(byte?)
X.N(default); // N(byte?)
X.N(null);    // N(byte?)

class X
{
    public static void M(int i32) { }
    public static void M(byte i8) { }

    public static void N(int? i32) { }
    public static void N(byte? i8) { }
}

The question is:

• Why is N(0) resolved as N(byte)? Accoding to the spec, 0 is int.
• Do you think it's OK that M(0) and M(default) behave differently?
• Is there any spec for M(default) is resolved as M(byte) and N(null) is N(byte?)?

[khm1600]

If my understanding of the spec is correct:

0 is int, therefore M(0) calls M(int).

default is not int or byte, int? or byte?, 0 and null are not int? or byte?, but all of them can be implicitly converted to the types, so they are resolved just like any other case where the expression converts to both types: the function whose parameter type implicitly converts to the parameter type of the other function is better.

spec:

6.4.5.3 Integer literals
The type of an integer literal is determined as follows:

• If the literal has no suffix, it has the first of these types in which its value can be represented: int, uint, long, ulong.

6.4.5.7 The null literal
A null_literal represents a null value. It does not have a type, but can be converted to any reference type or nullable value type through a null literal conversion (§10.2.7).

12.8.20 Default value expressions
A default_literal represents a default value (§9.3). It does not have a type, but can be converted to any type through a default literal conversion (§10.2.16).

12.6.4.3 Better function member
Given an argument list A with a set of argument expressions {E₁, E₂, ..., Eᵥ} and two applicable function members Mᵥ and Mₓ with parameter types {P₁, P₂, ..., Pᵥ} and {Q₁, Q₂, ..., Qᵥ}, Mᵥ is defined to be a better function member than Mₓ if

• for each argument, the implicit conversion from Eᵥ to Qᵥ is not better than the implicit conversion from Eᵥ to Pᵥ, and
• for at least one argument, the conversion from Eᵥ to Pᵥ is better than the conversion from Eᵥ to Qᵥ.

12.6.4.5 Better conversion from expression
Given an implicit conversion C₁ that converts from an expression E to a type T₁, and an implicit conversion C₂ that converts from an expression E to a type T₂, C₁ is a better conversion than C₂ if one of the following holds:

• E exactly matches T₁ and E does not exactly match T₂ (§12.6.4.6))
• E exactly matches both or neither of T₁ and T₂, and T₁ is a better conversion target than T₂ (§12.6.4.7))

12.6.4.7 Better conversion target
Given two types T₁ and T₂, T₁ is a better conversion target than T₂ if one of the following holds:

• An implicit conversion from T₁ to T₂ exists and no implicit conversion from T₂ to T₁ exists

[ufcpp]

Conversion to byte is better than to int? Smaller strage is better to covert?

[CyrusNajmabadi]

yes. consider something like

void Foo(Wide);
void Foo(Narrow);
Foo(narrowest);

Which would you expect that to go to? For example, say you had things like string vs object. Generally people would expect to call into the narrower of the two given both being applicable.

[ufcpp]

OK, now I understood the following sentence inplies that narrower is better.

An implicit conversion from T₁ to T₂ exists and no implicit conversion from T₂ to T₁ exists