Function FLMutableArray_GetMutableArray 

pub unsafe extern "C" fn FLMutableArray_GetMutableArray(
    arg1: FLMutableArray,
    index: u32,
) -> FLMutableArray

Convenience function for getting an array-valued property in mutable form.

• If the value for the key is not an array, returns NULL.
• If the value is a mutable array, returns it.
• If the value is an immutable array, this function makes a mutable copy, assigns the copy as the property value, and returns the copy.