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Designated initializers; template syntax for lambdas; range-based for loop with initializer.

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Anthony Calandra
2020-01-19 13:48:43 -05:00
parent 3489012600
commit ce454e0c2d
2 changed files with 66 additions and 2 deletions
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32
CPP20.md
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@@ -5,6 +5,9 @@ Many of these descriptions and examples come from various resources (see [Acknow
C++20 includes the following new language features:
- [concepts](#concepts)
- [designated initializers](#designated-initializers)
- [template syntax for lambdas](#template-syntax-for-lambdas)
- [range-based for loop with initializer](#range-based-for-loop-with-initializer)
C++20 includes the following new library features:
- [concepts library](#concepts-library)
@@ -163,6 +166,35 @@ concept C = requires(T x) {
```
See also: [concepts library](#concepts-library).
### Designated initializers
C-style designated initializer syntax. Any member fields that are not explicitly listed in the designated initializer list are default-initialized.
```c++
struct A {
int x;
int y;
int z = 123;
};
A a {.x = 1, .z = 2}; // a.x == 1, a.y == 0, a.z == 2
```
### Template syntax for lambdas
Use familiar template syntax in lambda expressions.
```c++
auto f = []<typename T>(std::vector<T> v) {
// ...
};
```
### Range-based for loop with initializer
This feature simplifies common code patterns, helps keep scopes tight, and offers an elegant solution to a common lifetime problem.
```c++
for (auto v = std::vector{1, 2, 3}; auto& e : v) {
std::cout << e;
}
// prints "123"
```
## C++20 Library Features
### Concepts library

36
README.md
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@@ -5,6 +5,9 @@ Many of these descriptions and examples come from various resources (see [Acknow
C++20 includes the following new language features:
- [concepts](#concepts)
- [designated initializers](#designated-initializers)
- [template syntax for lambdas](#template-syntax-for-lambdas)
- [range-based for loop with initializer](#range-based-for-loop-with-initializer)
C++20 includes the following new library features:
- [concepts library](#concepts-library)
@@ -255,6 +258,35 @@ concept C = requires(T x) {
```
See also: [concepts library](#concepts-library).
### Designated initializers
C-style designated initializer syntax. Any member fields that are not explicitly listed in the designated initializer list are default-initialized.
```c++
struct A {
int x;
int y;
int z = 123;
};
A a {.x = 1, .z = 2}; // a.x == 1, a.y == 0, a.z == 2
```
### Template syntax for lambdas
Use familiar template syntax in lambda expressions.
```c++
auto f = []<typename T>(std::vector<T> v) {
// ...
};
```
### Range-based for loop with initializer
This feature simplifies common code patterns, helps keep scopes tight, and offers an elegant solution to a common lifetime problem.
```c++
for (auto v = std::vector{1, 2, 3}; auto& e : v) {
std::cout << e;
}
// prints "123"
```
## C++20 Library Features
### Concepts library
@@ -433,8 +465,8 @@ y; // == 0
```
```c++
std::unordered_map<std::string, int> mapping {
{"a", 1},
{"b", 2},
{"a", 1},
{"b", 2},
{"c", 3},
};