StringToDouble was renamed
StringToMReal as part of code cleanup and the addition of several friends:
It should be as fast, but now in failure cases it returns a proper
Failure object instead of some bizarro-
$Failed[_String]. The error checking could be tighter (the new functions are more discriminating), but at least for now it will just truncate when it encounters invalid characters like the old
StringToDouble. Note that the
M in the names is for "Machine".
There shouldn't be an
Internal`StringToDouble, and I don't see it in a clean, standalone kernel. So perhaps some paclet that is multi-version is referencing and creating it.