How well do you know C++ auto type deduction?
6 comments
·December 9, 2025112233
Saving this to use as an argument when C++ comes up in a discussion. This toxic swamp cannot be fixed and anyone chosing to jump into it needs a warning.
CalChris
Apparently the C++ standard calls this type deduction. But I've always called it type inference.
Maxatar
Type deduction is a form of type inference, a very restricted/crude form of type inference that only considers the type of the immediate expression. The term is used in C++ because it predates the use of auto and was the term used to determine how to implicitly instantiate templates. auto uses exactly the same rules (with 1 single exception) as template type deduction, so the name was kept for familiarity. If instead of initializing a variable, you went through the examples on this website and passed the expression into a template function, the type would be deduced in exactly the same way with the exception of initializer lists.
Type inference is usually reserved for more general algorithms that can inspect not only how a variable is initialized, but how the variable used, such as what functions it's passed into, etc...
plq
Type inference is when you try to infer a type from its usage. ``auto`` does no such thing, it just copies a known type from source to target. Target has no influence over source's type.
null
Auto has really made c++ unapproachable to me. It's hard enough to reason about anything templated, and now I frequently see code where every method returns auto. How is any one supposed to do a code review without loading the patch into their IDE?