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Questions tagged [generic-lambda]

Generic Lambda lets Lambda function parameters be set to auto to let the compiler deduce the type. This generates a lambda type with a templated operator() so that the same lambda object can be invoked with any suitable type and a type-safe function with the right parameter type will be automatically generated.

Generic Lambda lets Lambda function parameters be set to auto to let the compiler deduce the type. This generates a lambda type with a templated operator() so that the same lambda object can be invoked with any suitable type and a type-safe function with the right parameter type will be automatically generated.

More Info : https://en.wikipedia.org/wiki/C%2B%2B14#Generic_lambdas

& https://isocpp.org/wiki/faq/cpp14-language#generic-lambdas

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Arity of a generic lambda

It is possible to deduce arity of a non-generic lambda by accessing its operator(). template struct fInfo : fInfo { }; template struct…
ScarletAmaranth
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Is it possible to static_assert that a lambda is not generic?

I implemented a Visit function (on a variant) that checks that the currently active type in the variant matches the function signature (more precisely the first argument). Based on this nice answer. For example #include #include…
NoSenseEtAl
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C++14: Generic lambda with generic std::function as class member

Consider this pseudo-snippet: class SomeClass { public: SomeClass() { if(true) { fooCall = [](auto a){ cout << a.sayHello(); }; } else { fooCall = [](auto b){ cout <<…
Juergen
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Generic lambdas with statically sized arrays as arguments

Is the following generic (polymorphic) lambda legal C++14? auto f = [](auto x[3]) { x[0]; x[1]; // etc. }; GCC and Clang 4 accept the code, but Visual Studio 2017 does not. Is it legal? error C3318: 'auto [3]': an array cannot have an…
Petter
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Using SFINAE with generic lambdas

Can generic lambdas take advantage of the "Substitution Failure Is Not An Error" rule ? Example auto gL = [](auto&& func, auto&& param1, auto&&... params) -> enable_if_t< is_integral< std::decay_t …
Nikos Athanasiou
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limits and uses of C++20 template lambas

A couple of related questions for C++ standard gurus. The incoming C++20 introduces template lambdas (P0428R2). So instead of auto x = [](auto x, auto y){ return x+y; }; we can specify the template parameter as follows auto x = [](T x,…
max66
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How to change the last argument in the parameter pack?

I have a function f1() template void f1(Args... args) { // the implementation is just an example, I don't really need a complicated // way to sum numbers boost::fusion::vector v(args...); std::cout <<…
facetus
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std::equal_range with lambda

Lets say I have a vector of strings and I want to find all strings, that start with 'a', so I can do this: struct cmp { bool operator()( const std::string &s, char c ) const { return s.front() < c; } bool operator()( char c, const…
Slava
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When use a function template instead of a generic lambda?

I can write a function template: template void f1(T parameter) { ... } But in C++14, I can also create a generic lambda: auto f2 = [](auto parameter) { ... }; Within f1 I can refer to T directly. Within f2, there's no T to refer to,…
KnowItAllWannabe
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generating calls to lambdas with arbitrary number of parameters

The following definition has proven to be very useful for me: template void apply_on_each_args(Func f, Args... args) { (f(args), ...); } Basically, the arguments pack folded on comma operator, allows to define several…
lrleon
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How to pass first N args to a C++ function

I've got a function like this: void loadData(std::function callback) { // data loading stuff callback(body, subject, header); } The problem is I'm not necessarily need to use subject and header…
Denis Sheremet
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Should non-capturing generic lambdas decay to function pointers?

Consider the following code: int main() { auto l = [](auto){}; void(*p)(int) = l; } It works just fine both with GCC and clang. Let's consider the following slightly modified version: int main() { auto l = [](auto...){}; …
skypjack
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return type deduction of recursive function

Recently, I read Barry's answer to this question Recursive lambda functions in C++11: template struct y_combinator { F f; // the lambda will be stored here // a forwarding operator(): template …
Jiashu Zou
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Clang claims constexpr member of generic lambda argument is not constexpr

I would like to write a generic lambda as a visitor for a variant. The members of this variant contain a constexpr member value, which I would like to use in the visitor. For example: #include template struct S { constexpr…
Claudius
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Generic std::function to store a generic lambda

When generic lambda is stored as a std::function, we need to provide a concrete type, something like, std::function thus binding to a specific type, The following declaration: std::function throws a compiler error. I…
Rajesh
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