c# 方法重载选择错误的重载并编译

Question

I have the following:

EnErrorCodes WriteToCard(EnRegs address, byte data)
EnErrorCodes WriteToCard(EnRegs address, ushort data)
EnErrorCodes WriteToCard(EnRegs address, uint data)
EnErrorCodes WriteToCard(EnRegs address, float data)
EnErrorCodes WriteToCard(EnRegs address, double data)

but had missed the ulong overload.

When then using the overloads blindly with a ulong , the compiler picked the float overload rather than throwing an error.

Took ages to work out why the system wasn't writing that data properly, only ctrl+clicking on the WriteToCard method where it was called then took it to the float overload.

Creating the ulong one obviously sorted it but I don't understand why it happened as it was a rather annoying feature to try and find.

Answer 1

This is because of Implicit numeric conversion .

If you look at highlighted part of above image, C# converts ulong to float , double , decimal .

As you have WriteToCard() with float parameter, if you pass data with ulong as a type, compiler implictly converts it to float and execute it, instead of throwing an error.

Answer 2

ulong can be implicitly converted to float and double , so there are two valid candidates for selecting method overload . The float one is selected because it is better conversion target :

Given two different types T1 and T2, T1 is a better conversion target than T2 if no implicit conversion from T2 to T1 exists, and at least one of the following holds:

• An implicit conversion from T1 to T2 exists
• ...

So there is no implicit conversion from double to float , but there is one from float to double