c++ - Share variable between two lambdas -


i want able share variable in containing scope between 2 lambda functions. have following:

void holdadd(const rect& rectangle, hold anonymousheld, hold anonymousfinish) {     std::map<int,bool> identifiercollection;      holdfinish holdfinish = [=](const int& identifier) mutable {         if (identifiercollection.count(identifier) == 0) return;          identifiercollection.erase(identifier);         anonymousfinish();     };      holdcollisioncollection.push_back([=](const int& identifier, const vec2& point) mutable {         if (rectangle.containspoint(point)) {             identifiercollection[identifier] = true;             anonymousheld();         } else {             holdfinish(identifier);         }     });     holdfinishcollection.push_back(holdfinish); }

i can see in debugger holdfinish pointing different implementation of identifiercollection in 2nd lambda function.

if use [=, &identifiercollection] throws exc_bad_access whether use mutable or not.

my experience other languages implement inline functions should possible. instance in javascript:

var = 10; var b = function() {     += 2; } var c = function() {     += 3; } b(); c(); alert(a);

would alert 15.

what have both lambda functions reference same identifiercollection implementation? behaves in same way javascript example.

unlike in scripting languages, identifiercollection's lifetime won't extended because captured closure. change [=] [&] capture reference, it's dangling reference local variable you're capturing.

you'll have manage lifetime of identifiercollection yourself; frankly, sounds perfect opportunity shared pointer, captured value each lambda. dynamically-allocated map wraps literally exist long need to.

void holdadd(const rect& rectangle, hold anonymousheld, hold anonymousfinish) {     auto identifiercollection = std::make_shared<std::map<int,bool>>();      holdfinish holdfinish = [=](const int& identifier) mutable {         if (identifiercollection->count(identifier) == 0) return;          identifiercollection->erase(identifier);         anonymousfinish();     };      holdcollisioncollection.push_back([=](const int& identifier, const vec2& point) mutable {         if (rectangle.containspoint(point)) {             (*identifiercollection)[identifier] = true;             anonymousheld();         } else {             holdfinish(identifier);         }     });     holdfinishcollection.push_back(holdfinish); }

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