Tutorial by Examples: capture

If you need to extract a part of string from the input string, we can use capture groups of regex. For this example, we'll start with a simple phone number regex: \d{3}-\d{3}-\d{4} If parentheses are added to the regex, each set of parentheses is considered a capturing group. In this case, we a...

class MyClass { func sayHi() { print("Hello") } deinit { print("Goodbye") } } When a closure captures a reference type (a class instance), it holds a strong reference by default: let closure: () -> Void do { let obj = MyClass() // Captures a strong re...

If you specify the variable's name in the capture list, the lambda will capture it by value. This means that the generated closure type for the lambda stores a copy of the variable. This also requires that the variable's type be copy-constructible: int a = 0; [a]() { return a; // Ok, 'a' ...

C++14 Lambdas can capture expressions, rather than just variables. This permits lambdas to store move-only types: auto p = std::make_unique<T>(...); auto lamb = [p = std::move(p)]() //Overrides capture-by-value of `p`. { p->SomeFunc(); }; This moves the outer p variable into th...

If you precede a local variable's name with an &, then the variable will be captured by reference. Conceptually, this means that the lambda's closure type will have a reference variable, initialized as a reference to the corresponding variable from outside of the lambda's scope. Any use of the v...

By default, local variables that are not explicitly specified in the capture list, cannot be accessed from within the lambda body. However, it is possible to implicitly capture variables named by the lambda body: int a = 1; int b = 2; // Default capture by value [=]() { return a + b; }; // OK;...

A group is a section of a regular expression enclosed in parentheses (). This is commonly called "sub-expression" and serves two purposes: It makes the sub-expression atomic, i.e. it will either match, fail or repeat as a whole. The portion of text it matched is accessible in the remai...

A lambda expression evaluated in a class' member function is implicitly a friend of that class: class Foo { private: int i; public: Foo(int val) : i(val) {} // definition of a member function void Test() { auto lamb = [](Foo &foo, int val) ...

Some regular expression flavors allow named capture groups. Instead of by a numerical index you can refer to these groups by name in subsequent code, i.e. in backreferences, in the replace pattern as well as in the following lines of the program. Numerical indexes change as the number or arrangemen...

Given the flavors, the named capture group may looks like this: (?'name'X) (?<name>X) (?P<name>X) With X being the pattern you want to capture. Let's consider the following string: Once upon a time there was a pretty little girl... Once upon a time there was a unicorn with an h...

As you may (or not) know, you can reference a capture group with: $1 1 being the group number. In the same way, you can reference a named capture group with: ${name} \{name} g\{name} Let's take the preceding example and replace the matches with The hero of the story is a ${subject}. T...

The pattern matching library trivia provides a system trivia.ppcre that allows captured groups to be bound through pattern matching (trivia:match "John Doe" ((trivia.ppcre:ppcre "(.*)\\W+(.*)" first-name last-name) (list :first-name first-name :last-name last-name))) ;...

Use & to capture functions from other modules. You can use the captured functions directly as function parameters or within anonymous functions. Enum.map(list, fn(x) -> String.capitalize(x) end) Can be made more concise using &: Enum.map(list, &String.capitalize(&1)) Captu...

Match (node_name:node_type {}), (node_name_two:node_type_two {}) CREATE (node_name)-[::edge_name{}]->(node_name_two)

If you want to change the order of a character strings you can use parentheses in the pattern to group parts of the string together. These groups can in the replacement argument be addresed using consecutive numbers. The following example shows how you can reorder a vector of names of the form &quo...

Functions which return a character vector Base R has two functions for invoking a system command. Both require an additional parameter to capture the output of the system command. system("top -a -b -n 1", intern = TRUE) system2("top", "-a -b -n 1", stdout = TRUE) ...

This is a .NET regex specific modifier expressed with n. When used, unnamed groups (like (\d+)) are not captured. Only valid captures are explicitly named groups (e.g. (?<name> subexpression)). (?n)(\d+)-(\w+)-(?<id>\w+) will match the whole 123-1_abc-00098, but (\d+) and (\w+) won't...

a='I am a simple string with digits 1234' pat='(.*) ([0-9]+)' [[ "$a" =~ $pat ]] echo "${BASH_REMATCH[0]}" echo "${BASH_REMATCH[1]}" echo "${BASH_REMATCH[2]}" Output: I am a simple string with digits 1234 I am a simple string with digits 1234

Creating a WebM video from canvas frames and playing in canvas, or upload, or downloading. Example capture and play canvas name = "CanvasCapture"; // Placed into the Mux and Write Application Name fields of the WebM header quality = 0.7; // good quality 1 Best < 0.7 ok to poor fps =...

The substrings captured by capture groups are accessible from RegexMatch objects using indexing notation. For instance, the following regex parses North American phone numbers written in (555)-555-5555 format: julia> phone = r"\((\d{3})\)-(\d{3})-(\d{4})" and suppose we wish to ext...