lambda

问题 I have a dataframe, one column is a URL, the other is a name. I'm simply trying to add a third column that takes the URL, and creates an HTML link. The column newsSource has the Link name, and url has the URL. For each row in the dataframe, I want to create a column that has: <a href="[the url]">[newsSource name]</a> Trying the below throws the error File "C:\Users\AwesomeMan\Documents\Python\MISC\News Alerts\simple_news.py", line 254, in df['sourceURL'] = df['url'].apply(lambda x: '{1}'

问题 Is there a way to make a lambda decay to a pointer, without explicitly casting to the right signature? This would tidy some code: template<typename T> T call(T(*func)()){ return func(); } int ptr(){ return 0; } int main(){ auto ret1 = call(ptr); auto ret2 = call((int(*)())([]{ return 0; })); auto ret3 = call([]{ return 0; }); //won't compile } It's evident that a call to call works only if the lambda decays to a pointer, but I'm guessing that that can happen only after the right function

问题 Is there a way to make a lambda decay to a pointer, without explicitly casting to the right signature? This would tidy some code: template<typename T> T call(T(*func)()){ return func(); } int ptr(){ return 0; } int main(){ auto ret1 = call(ptr); auto ret2 = call((int(*)())([]{ return 0; })); auto ret3 = call([]{ return 0; }); //won't compile } It's evident that a call to call works only if the lambda decays to a pointer, but I'm guessing that that can happen only after the right function

问题 This topic is may be dublicated. I asked in a different scenario under this topic and it is answered by Derviş Kayımbaşıoğlu. When I edited my topic like this and asked again, Derviş Kayımbaşıoğlu said I should ask this in a new topic. So I had to ask the question in a new topic. Here is data schema example: I have a list getting from the SQLite database like this: var decisions = _db.decisions.Where(x => x.CAT_ID == Cat.Id).ToList(); If the values of the REC_ID field in this list are the

问题 This topic is may be dublicated. I asked in a different scenario under this topic and it is answered by Derviş Kayımbaşıoğlu. When I edited my topic like this and asked again, Derviş Kayımbaşıoğlu said I should ask this in a new topic. So I had to ask the question in a new topic. Here is data schema example: I have a list getting from the SQLite database like this: var decisions = _db.decisions.Where(x => x.CAT_ID == Cat.Id).ToList(); If the values of the REC_ID field in this list are the

问题 I am looking into Blazor and I stumbpled on this expression: @onclick="(() => SomeMethod(parameter))" I cannot find/google anywhere what does this (I guess lambda) expression is actually doing. Can anybody explain me please this part: () => and why to use it and where? EDIT: What is the difference between the above and this: @onclick="SomeMethod(parameter)" 回答1: () =>() is basically a lambda function. Imagine you have a function delegate (int foo) { return foo*2}; this can be rewritten as

问题 I am looking into Blazor and I stumbpled on this expression: @onclick="(() => SomeMethod(parameter))" I cannot find/google anywhere what does this (I guess lambda) expression is actually doing. Can anybody explain me please this part: () => and why to use it and where? EDIT: What is the difference between the above and this: @onclick="SomeMethod(parameter)" 回答1: () =>() is basically a lambda function. Imagine you have a function delegate (int foo) { return foo*2}; this can be rewritten as

问题 (Realted to this other question of mine; if you give a look at that too, I would really appreciate it.) If std::array<T,N>::size is constexpr, then why does the following code not even compile? #include <array> #include <iostream> constexpr auto print_size = [](auto const& array){ constexpr auto size = array.size(); std::cout << size << '\n'; }; int main() { print_size(std::array<int,3>{{1,2,3}}); } The error is the following: $ g++ -std=c++17 deleteme.cpp && ./a.out deleteme.cpp: In

问题 As per the Documentation, Method Reference is absolutely not a static call. It works on both static and non- static methods. When we define our own non-static method in a given class and try to use it using Method Reference then the compile-time-error "cannot make static reference to non static method" is NOT seen in case of Function but only seen in case of Supplier, Consumer and Predicate. Why is that so? class Demo{ private Function<Student, Integer> p= Student::getGradeLevel; // fine

问题 As per the Documentation, Method Reference is absolutely not a static call. It works on both static and non- static methods. When we define our own non-static method in a given class and try to use it using Method Reference then the compile-time-error "cannot make static reference to non static method" is NOT seen in case of Function but only seen in case of Supplier, Consumer and Predicate. Why is that so? class Demo{ private Function<Student, Integer> p= Student::getGradeLevel; // fine