From c21cf5a1e230dadf81bc4e31e2d2f9133551b365 Mon Sep 17 00:00:00 2001 From: Geoff Liu Date: Mon, 4 May 2015 02:40:04 -0600 Subject: Templates and such --- c++.html.markdown | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 102 insertions(+) (limited to 'c++.html.markdown') diff --git a/c++.html.markdown b/c++.html.markdown index ae93ceba..10c39c9c 100644 --- a/c++.html.markdown +++ b/c++.html.markdown @@ -432,6 +432,81 @@ int main () { return 0; } +///////////////////// +// Templates +///////////////////// + +// Templates in C++ are mostly used for generic programming, though they are +// much more powerful than generics constructs in other languages. It also +// supports explicit and partial specialization, functional-style type classes, +// and also it's Turing-complete. + +// We start with the kind of generic programming you might be familiar with. To +// define a class or function that takes a type parameter: +template +class Box { + // In this class, T can be used as any other type. + void insert(const T&) { ... } +}; + +// During compilation, the compiler actually generates copies of each template +// with parameters substituted, and so the full definition of the class must be +// present at each invocation. This is why you will see template classes defined +// entirely in header files. + +// To instantiate a template class on the stack: +Box intBox; + +// and you can use it as you would expect: +intBox.insert(123); + +// You can, of course, nest templates: +Box > boxOfBox; +boxOfBox.insert(intBox); + +// Up until C++11, you muse place a space between the two '>'s, otherwise '>>' +// will be parsed as the right shift operator. + +// You will sometimes see +// template +// instead. The 'class' keyword and 'typename' keyword are _mostly_ +// interchangeable in this case. For full explanation, see +// http://en.wikipedia.org/wiki/Typename +// (yes, that keyword has its own Wikipedia page). + +// Similarly, a template function: +template +void barkThreeTimes(const T& input) +{ + input.bark(); + input.bark(); + input.bark(); +} + +// Notice that nothing is specified about the type parameters here. The compiler +// will generate and then type-check every invocation of the template, so the +// above function works with any type 'T' that has a const 'bark' method! + +Dog fluffy; +fluffy.setName("Fluffy") +barkThreeTimes(fluffy); Prints "Fluffy barks" three times. + +// Template parameters don't have to be classes, though this is used very rarely: +template +void printMessage() { + cout << "Learn C++ in " << Y << " minutes!" << endl; +} + +// And you can explicitly specialize templates for more efficient code: +template<> +void printMessage<10>() { + cout << "Learn C++ faster in only 10 minutes!" << endl; +} + +printMessage<20>(); // Prints "Learn C++ in 20 minutes!" +printMessage<10>(); // Prints "Learn C++ faster in only 10 minutes!" + + ///////////////////// // Exception Handling ///////////////////// @@ -585,6 +660,33 @@ void doSomethingWithAFile(const std::string& filename) // vector (i.e. self-resizing array), hash maps, and so on // all automatically destroy their contents when they fall out of scope. // - Mutexes using lock_guard and unique_lock + + +///////////////////// +// Fun stuff +///////////////////// + +// Aspects of C++ that may be surprising to newcomers (and even some veterans): + +// You can override private methods! +class Foo { + virtual void bar(); +}; +class FooSub : public Foo { + virtual void bar(); // overrides Foo::bar! +}; + +// 0, false, NULL are all the same thing! +bool* pt = new bool; +*pt = 0; // Sets the value points by 'pt' to false. +pt = 0; // Sets 'pt' to the null pointer. Yes both lines compile without warning. + +// '=' != '=' +Foo f1 = f2; // Calls Foo::Foo(const Foo&) or some variant copy constructor. + +Foo f1; +f1 = f2; // Calls Foo::operator=(Foo&) or variant. + ``` Futher Reading: -- cgit v1.2.3 From 05c2617aaf6d040b1e4372d8f83df11288ff2279 Mon Sep 17 00:00:00 2001 From: Geoff Liu Date: Mon, 4 May 2015 02:45:31 -0600 Subject: Minor fix --- c++.html.markdown | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'c++.html.markdown') diff --git a/c++.html.markdown b/c++.html.markdown index 10c39c9c..e50c33fa 100644 --- a/c++.html.markdown +++ b/c++.html.markdown @@ -489,15 +489,16 @@ void barkThreeTimes(const T& input) Dog fluffy; fluffy.setName("Fluffy") -barkThreeTimes(fluffy); Prints "Fluffy barks" three times. +barkThreeTimes(fluffy); // Prints "Fluffy barks" three times. -// Template parameters don't have to be classes, though this is used very rarely: +// Template parameters don't have to be classes: template void printMessage() { cout << "Learn C++ in " << Y << " minutes!" << endl; } -// And you can explicitly specialize templates for more efficient code: +// And you can explicitly specialize templates for more efficient code (most +// real-world uses of specialization are not as trivial as this): template<> void printMessage<10>() { cout << "Learn C++ faster in only 10 minutes!" << endl; -- cgit v1.2.3 From 6c635d1c3e5bb88940fb0afb01218d2e7d3f11c0 Mon Sep 17 00:00:00 2001 From: Geoff Liu Date: Tue, 5 May 2015 00:45:14 -0600 Subject: Response to comments --- c++.html.markdown | 39 +++++++++++++++++++++++++++++++-------- 1 file changed, 31 insertions(+), 8 deletions(-) (limited to 'c++.html.markdown') diff --git a/c++.html.markdown b/c++.html.markdown index e50c33fa..517ce367 100644 --- a/c++.html.markdown +++ b/c++.html.markdown @@ -497,8 +497,10 @@ void printMessage() { cout << "Learn C++ in " << Y << " minutes!" << endl; } -// And you can explicitly specialize templates for more efficient code (most -// real-world uses of specialization are not as trivial as this): +// And you can explicitly specialize templates for more efficient code. Of +// course, most real-world uses of specialization are not as trivial as this. +// Note that you still need to declare the function (or class) as a template +// even if you explicitly specified all parameters. template<> void printMessage<10>() { cout << "Learn C++ faster in only 10 minutes!" << endl; @@ -667,7 +669,9 @@ void doSomethingWithAFile(const std::string& filename) // Fun stuff ///////////////////// -// Aspects of C++ that may be surprising to newcomers (and even some veterans): +// Aspects of C++ that may be surprising to newcomers (and even some veterans). +// This section is, unfortunately, wildly incomplete; C++ is one of the easiest +// languages with which to shoot yourself in the foot. // You can override private methods! class Foo { @@ -677,16 +681,35 @@ class FooSub : public Foo { virtual void bar(); // overrides Foo::bar! }; -// 0, false, NULL are all the same thing! + +// 0 == false == NULL (most of the time)! bool* pt = new bool; *pt = 0; // Sets the value points by 'pt' to false. -pt = 0; // Sets 'pt' to the null pointer. Yes both lines compile without warning. +pt = 0; // Sets 'pt' to the null pointer. Both lines compile without warnings. + +// nullptr is supposed to fix some of that issue: +int* pt2 = new int; +*pt2 = nullptr; // Doesn't compile +pt2 = nullptr; // Sets pt2 to null. + +// But somehow 'bool' type is an exception. +*pt = nullptr; // This still compiles, even though '*pt' is a bool! + + +// '=' != '=' != '='! +// Calls Foo::Foo(const Foo&) or some variant copy constructor. +Foo f2; +Foo f1 = f2; -// '=' != '=' -Foo f1 = f2; // Calls Foo::Foo(const Foo&) or some variant copy constructor. +// Calls Foo::Foo(const Foo&) or variant, but only copies the 'Foo' part of +// 'fooSub'. Any extra members of 'fooSub' are discarded. This lovely behavior +// is called "object slicing." +FooSub fooSub; +Foo f1 = fooSub; +// Calls Foo::operator=(Foo&) or variant. Foo f1; -f1 = f2; // Calls Foo::operator=(Foo&) or variant. +f1 = f2; ``` Futher Reading: -- cgit v1.2.3 From 25bd06d77a70964acfbdbf8a7c7a50eb312eae9f Mon Sep 17 00:00:00 2001 From: Geoff Liu Date: Wed, 6 May 2015 15:25:28 -0600 Subject: comment changes --- c++.html.markdown | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'c++.html.markdown') diff --git a/c++.html.markdown b/c++.html.markdown index 517ce367..66d4aeb1 100644 --- a/c++.html.markdown +++ b/c++.html.markdown @@ -692,7 +692,7 @@ int* pt2 = new int; *pt2 = nullptr; // Doesn't compile pt2 = nullptr; // Sets pt2 to null. -// But somehow 'bool' type is an exception. +// But somehow 'bool' type is an exception (this is to make `if (ptr)` compile). *pt = nullptr; // This still compiles, even though '*pt' is a bool! @@ -702,8 +702,8 @@ Foo f2; Foo f1 = f2; // Calls Foo::Foo(const Foo&) or variant, but only copies the 'Foo' part of -// 'fooSub'. Any extra members of 'fooSub' are discarded. This lovely behavior -// is called "object slicing." +// 'fooSub'. Any extra members of 'fooSub' are discarded. This sometimes +// horrifying behavior is called "object slicing." FooSub fooSub; Foo f1 = fooSub; -- cgit v1.2.3