ram@zedat.fu-berlin.de (Stefan Ram) writes:

ram@zedat.fu-berlin.de (Stefan Ram) wrote or quoted:

inspect (mystr) {
"hello" => { /* ... */ },

Why there is no string "switch" statement in C++

C++ is a systems programming language with zero-cost abstraction.

The core language consists of predictable, low-level primitives
(like "if", "while", "switch", or "+") that map to basic machine
instructions and require minimal runtime overhead.

If a native C++ inspect statement allowed matching a string variable
against string cases, a single "primitive-looking" statement would
actually execute an O(N) string-comparison loop at runtime. Depending
on how the compiler tries to optimize it, it might generate a sequen-
tial chain of string comparisons, a trie structure, or a hashing rou-
tine.

Introducing a feature into the core language grammar that can intro-
spect, match, and switch on complex string types blurs the historical boundary between lightweight primitive instructions in the core lan-
guage and complex library types, making it more difficult for program-
mers to "see" the run-time costs of core language features.

std::cout << x << '\n';

This looks like it's just using core language features, but it can
result in arbitrarily complex actions because operator<< is overloaded.
There are plenty of other examples.

The fact that C++ doesn't currently have switch on strings or equivalent doesn't greatly bother me, but if such a feature were added it would be consistent with a lot of other high-level C++ features that look like
core language syntax. (And presumably it would be designed to work
on arbitrary types, not just strings.)

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */

--- PyGate Linux v1.5.19
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On Sat, 19 Sep 2026 15:42:32 -0700
Keith Thompson <Keith.S.Thompson+u@gmail.com> gabbled:

consistent with a lot of other high-level C++ features that look like
core language syntax. (And presumably it would be designed to work
on arbitrary types, not just strings.)

Indeed. As I said in an earlier post the object class being switched on would simply need to implement operator==() else the compiler would error.


--- PyGate Linux v1.5.19
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)

On 20/09/2026 09:36, boltar@caprica.universe wrote:

On Sat, 19 Sep 2026 15:42:32 -0700
Keith Thompson <Keith.S.Thompson+u@gmail.com> gabbled:

consistent with a lot of other high-level C++ features that look like
core language syntax. (And presumably it would be designed to work
on arbitrary types, not just strings.)

Indeed. As I said in an earlier post the object class being switched on would simply need to implement operator==() else the compiler would error.

Yes.

It is conceivable that a compiler could take advantage of additional
features of the class, such as order operators or constexpr hashes, in
order to generate more efficient match/switch code. (Just as they may generate binary trees or tables for today's switches.) But that would
be transparent to the user - a "==" operator is the base.



--- PyGate Linux v1.5.19
* Origin: Dragon's Lair, PyGate NNTP<>Fido Gate (3:633/10)