Search code examples
c++arraysindexingindexernot-operator

What does an exclamation mark in array index do?

While perusing through my organization's source repository I came across this little gem:

RawParameterStorage[!ParameterWorkingIdx][ParameterDataOffset] = ...

Is this valid code? (It compiles) What does the exclamation mark here do?

An invert ~ operator might make sense, since it's commonly confused with the not ! operator in boolean expressions. However, it doesn't seem to make logical sense to impose the not ! operator on an array index. Any Thoughts?

Solution

  • !ParameterWorkingIdx Means ParameterWorkingIdx is 0, If it is, !ParameterWorkingIdx evaluates as true which might be implicitly converted to the indexer type (For example, 1 for integer indexer as in an array), otherwise, it evaluates as false.

    • If ParameterWorkingIdx == 0 then [!ParameterWorkingIdx] == [1].

    • If ParameterWorkingIdx != 0 then [!ParameterWorkingIdx] == [0].

    It also depends on other stuff like:

    • The type of ParameterWorkingIdx.

    • overloading of ! operator by the type of ParameterWorkingIdx.

    • indexer overloading by the type of RawParameterStorage.

    • etc...