A closure captures the variables it uses from the surrounding scope. By default, the compiler infers the least restrictive capture: an immutable borrow if the closure only reads the variable, a mutable borrow if it modifies it, and a move if the closure takes ownership. The inference is convenient for the closures that are called…
A closure is an anonymous function that can capture the variables from the scope where it is defined. It is the fundamental tool for the higher-order functions, the callbacks, and the concise inline logic. The |x| x + 1 is a closure that takes the x and returns the x + 1, and unlike the…
Every command-line tool has an interface. The user types the program name, the options, the positional arguments, and the subcommands, and the program must parse the input, validate it, and produce a helpful error message when something is wrong. Hand-writing this parsing is tedious and error-prone. The argument order, the short and long forms, the…
A unit test verifies a function in isolation. An integration test verifies the library as the consumer uses it. The unit tests live in the src/ files, and they can access the private items. The integration tests live in the tests/ directory, and each file is a separate crate that depends on the library. The…
Rust treats testing as a first-class part of the language. The cargo test command is built into the toolchain, the test functions are ordinary functions annotated with the #[test] attribute, and the test module is the ordinary module with the #[cfg(test)] attribute. There is no separate test framework to install, no configuration file to write,…
A unit test should test one thing. When the unit under the test depends on the database, the network, the clock, or the file system, the test must isolate the unit from those dependencies. Otherwise the test is slow, flaky, and coupled to the external systems. Test doubles are the objects that stand in for…
A unit test is a small program that exercises one piece of the code and asserts the expected result. The package:test is the standard testing framework for the Dart, and it provides the test function, the group function, the expect function, and the matchers. The framework runs the tests, collects the results, and reports the…
Manual JSON serialization is verbose. For every model class, the developer writes the fromJson factory, the toJson method, and the mapping between the JSON fields and the Dart fields. The mapping is repetitive, and it is easy to get wrong when a field is added or renamed. The json_serializable package generates the mapping from the…
JSON is the wire format of the modern web. The REST APIs return it, the configuration files store it, the WebSocket messages carry it, and the local storage persists it. The dart:convert library is the built-in codec for the JSON, and it provides the two functions: the jsonEncode and the jsonDecode. The jsonEncode takes the…
A Dart application that talks to a REST API has two options. The first is the dart:io library, which provides the HttpClient class and works on the Dart VM, the server, the command-line tools, and the mobile applications. The HttpClient is the low-level, the full-featured client: it handles the persistent connections, the cookies, the authentication,…