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0 pointsa_t483y ago0 comments

C++ still has this problem - std::unordered_map<std::string, std::string>` and `std::unordered_map<std::string, const std::string>` are basically unrelated types - you can't const-cast the templated const away. (I may be misunderstanding here)

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masklinn3y ago

> you can't const-cast the templated const away.

That seems like a good thing. If you're handed a map to const values you can't just go "imma gunna mutate them anyway".

a_t48OP3y ago

Yup, it's definitely a bit of a code smell if you do. The issue is more the reverse, though - I can't make a mutable map, then hand it by pointer/reference to something that says it wants an immutable map later.

masklinn3y ago

Not necessarily a bad thing either, things can get odd if you're not the only owner and it's mutated under you unexpectedly.

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morelisp3y ago

Normally (when containers are not involved) this is exactly the point of a const cast.

account423y ago

No, the primary point of a const cast is "I need to pass this to an API that expects a non-const pointer even though it won't mutate it".

Casting const away and then mutating is a footgun as you are in undefined behavior territory as soon as your pointer/reference is not just const itself but points to a const variable.

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masklinn3y ago

> you can't const-cast the templated const away.

That seems like a good thing. If you're handed a map to const values you can't just go "imma gunna mutate them anyway".

a_t48OP3y ago

masklinn3y ago

Not necessarily a bad thing either, things can get odd if you're not the only owner and it's mutated under you unexpectedly.

2 more replies

morelisp3y ago

Normally (when containers are not involved) this is exactly the point of a const cast.

account423y ago

No, the primary point of a const cast is "I need to pass this to an API that expects a non-const pointer even though it won't mutate it".

Casting const away and then mutating is a footgun as you are in undefined behavior territory as soon as your pointer/reference is not just const itself but points to a const variable.

j / k navigate · click thread line to collapse