20 ms·

This doesn't function as an interface though. You cannot pass a FooBar to a function that expects a Foo, for example, and although you can fairly easily referen

by sltkr 2y ago

This doesn't function as an interface though. You cannot pass a FooBar to a function that expects a Foo, for example, and although you can fairly easily reference the Foo-part of a FooBar instance (`foobar.Foo`) there is no way to pass e.g. an array of FooBar instances to a function that takes a slice of Foo[] as its argument. That's the problem to be solved.

lenkite 2y ago
Ok, Go generics is pretty limited but you can achieve this in C++ via concepts. #include <iostream> #include <string> #include <type_traits> // Concept to check for 'foo' field of type int template <typename T> concept HasFooInt = requires(T t) { { t.foo } -> std::convertible_to<int>; }; // Concept to check for 'bar' field of type string template <typename T> concept HasBarString = requires(T t) { { t.bar } -> std::convertible_to<std::string>; }; // Generic function that accepts T with either 'foo' or 'bar' template <typename T> requires HasFooInt<T> || HasBarString<T> void printField(const T& t) { if constexpr (HasFooInt<T>) { std::cout << "foo: " << t.foo << std::endl; } else if constexpr (HasBarString<T>) { std::cout << "bar: " << t.bar << std::endl; } } struct Foo { int foo; }; struct Bar { std::string bar; }; struct FooBar { int foo; std::string bar; }; int main() { Foo s1 { 42 }; Bar s2 { "hello" }; FooBar s3 { 100, "world" }; printField(s1); // prints: foo: 42 printField(s2); // prints: bar: hello printField(s3); // prints: foo: 100 (prefers foo due to order of checks) return 0; }
shhsshs 2y ago
Totally achievable by using interfaces instead of structs type Foo interface { Foo() int } type Bar interface { Bar() string } type FooBar interface { Foo Bar } Then functions that accept a Foo will also happily take a FooBar. Does not solve the problem of passing a FooBar[] to a function that expects Foo[] but that can be solved with generics or a simple function to convert FooBar[] to Foo[].

by sltkr 2y ago

lenkite 2y ago

Ok, Go generics is pretty limited but you can achieve this in C++ via concepts. #include <iostream> #include <string> #include <type_traits> // Concept to check for 'foo' field of type int template <typename T> concept HasFooInt = requires(T t) { { t.foo } -> std::convertible_to<int>; }; // Concept to check for 'bar' field of type string template <typename T> concept HasBarString = requires(T t) { { t.bar } -> std::convertible_to<std::string>; }; // Generic function that accepts T with either 'foo' or 'bar' template <typename T> requires HasFooInt<T> || HasBarString<T> void printField(const T& t) { if constexpr (HasFooInt<T>) { std::cout << "foo: " << t.foo << std::endl; } else if constexpr (HasBarString<T>) { std::cout << "bar: " << t.bar << std::endl; } } struct Foo { int foo; }; struct Bar { std::string bar; }; struct FooBar { int foo; std::string bar; }; int main() { Foo s1 { 42 }; Bar s2 { "hello" }; FooBar s3 { 100, "world" }; printField(s1); // prints: foo: 42 printField(s2); // prints: bar: hello printField(s3); // prints: foo: 100 (prefers foo due to order of checks) return 0; }

shhsshs 2y ago

Totally achievable by using interfaces instead of structs type Foo interface { Foo() int } type Bar interface { Bar() string } type FooBar interface { Foo Bar } Then functions that accept a Foo will also happily take a FooBar. Does not solve the problem of passing a FooBar[] to a function that expects Foo[] but that can be solved with generics or a simple function to convert FooBar[] to Foo[].