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When can I use a forward declaration?

...are a member to be a pointer or a reference to the incomplete type: class Foo { X *p; X &r; }; Declare functions or methods which accept/return incomplete types: void f1(X); X f2(); Define functions or methods which accept/return pointers/references to the incomplete type (but wit...
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What is the difference between 'typedef' and 'using' in C++11?

...C++03) (init. statement in for loop iteration statements). for(typedef int Foo; Foo{} != 0;) {} // C++17 (if and switch initialization statements). if (typedef int Foo; true) { (void)Foo{}; } // ^^^^^^^^^^^^^^^ init-statement switch(typedef int Foo; 0) { case 0: (void)Foo{}; } // ^^^^^^^^^^^^...
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SELECT DISTINCT on one column

...RDER BY ID) AS RowNumber FROM MyTable WHERE SKU LIKE 'FOO%') AS a WHERE a.RowNumber = 1 share | improve this answer | follow | ...
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Find when a file was deleted in Git

... Git repository in /home/mark/example/.git/ mark@lunchbox:~/example$ touch foo && git add foo && git commit -m "Added foo" [master (root-commit) ddff7a7] Added foo 1 file changed, 0 insertions(+), 0 deletions(-) create mode 100644 foo mark@lunchbox:~/example$ git checkout -b newbra...
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Circular (or cyclic) imports in Python

... If you do import foo (inside bar.py) and import bar (inside foo.py), it will work fine. By the time anything actually runs, both modules will be fully loaded and will have references to each other. The problem is when instead you do from foo ...
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What techniques can be used to speed up C++ compilation times?

...ample, if you have a class, template <typename T, typename U> struct foo { }; and both of T and U can have 10 different options, you have increased the possible template instantiations of this class to 100. One way to resolve this is to abstract the common part of the code to a different clas...
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How to escape braces (curly brackets) in a format string in .NET

... For you to output foo {1, 2, 3} you have to do something like: string t = "1, 2, 3"; string v = String.Format(" foo {{{0}}}", t); To output a { you use {{ and to output a } you use }}. or Now, you can also use c# string interpolation like ...
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List changes unexpectedly after assignment. How do I clone or copy it to prevent this?

...-needing method, but sometimes unavoidable. Example: import copy class Foo(object): def __init__(self, val): self.val = val def __repr__(self): return 'Foo({!r})'.format(self.val) foo = Foo(1) a = ['foo', foo] b = a.copy() c = a[:] d = list(a) e = copy.copy(a) f = cop...
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What does a lazy val do?

...pendent or cyclic structures. E.g. this leads to an stack overflow: trait Foo { val foo: Foo } case class Fee extends Foo { val foo = Faa() } case class Faa extends Foo { val foo = Fee() } println(Fee().foo) //StackOverflowException But with lazy vals it works fine trait Foo { val foo: Foo } ca...
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Inserting a string into a list without getting split into characters

... To add to the end of the list: list.append('foo') To insert at the beginning: list.insert(0, 'foo') share | improve this answer | follow ...