static struct AliasedString { string s; alias s this; } enum StringEnum { a = "foo" } assert(!isConvertibleToString!string); assert(isConvertibleToString!AliasedString); assert(isConvertibleToString!StringEnum); assert(isConvertibleToString!(char[25])); assert(!isConvertibleToString!(char[]));
Warning: This trait will be deprecated as soon as it is no longer used in Phobos. For a function parameter to safely accept a type that implicitly converts to string as a string, the conversion needs to happen at the callsite; otherwise, the conversion is done inside the function, and in many cases, that means that local memory is sliced (e.g. if a static array is passed to the function, then it's copied, and the resulting dynamic array will be a slice of a local variable). So, if the resulting string escapes the function, the string refers to invalid memory, and accessing it would mean accessing invalid memory. As such, the only safe way for a function to accept types that implicitly convert to string is for the implicit conversion to be done at the callsite, and that can only occur if the parameter is explicitly typed as an array, whereas using isConvertibleToString in a template constraint would result in the conversion being done inside the function. As such, isConvertibleToString is inherently unsafe and is going to be deprecated.
Detect whether T is a struct, static array, or enum that is implicitly convertible to a string.