System

The standard library: collections (List, Dictionary, HashSet, Stack, Queue), text (StringBuilder, Encoding, Regex, JsonValue), files and folders (File, Directory, Path, FileStream, StreamReader, StreamWriter), time (DateTime, TimeSpan, Stopwatch), processes, random numbers and threads (Thread, Mutex).

using System;

int Main()
{
    var names = List<string>.Create();
    names.Add("Ann");
    Console.WriteLine(names[0]);
    return 0;
}

Functions that can fail return typed results, e.g. IoError<string> from File.ReadAllText: the value or one of the codes of an error enum (IoError, ParseError, EncodingError, JsonError, RegexError).

Types

Type	Description
TimeSpan	A duration (or a time of day): a signed number of ticks of 100 ns, like .NET’s TimeSpan (with methods instead of properties).
DateTime	A date and time of day, local or UTC.
Stopwatch	Measures elapsed time with the monotonic clock of the system (not affected by changes of the time of day).
KeyValuePair<TKey,	A key and its value, from Dictionary<TKey, TValue>.Entries.
Dictionary<TKey,	A hash table (separate chaining).
Path	File names and paths, as strings: Path.Combine("src", "main.cshift"), Path.GetExtension(file), …
Directory	Directories and file names.
Encoding	Conversion between strings (always UTF-8 in memory) and raw bytes.
File	Whole files: reading, writing, copying, moving and deleting them (static functions).
HashSet<T>	A set of values (T must be a valid Dictionary key: numbers, bool, char, enums, string, or a struct with GetHashCode/Equals).
JsonValue	Reading (Json.Parse), building and writing (JsonValue.ToString / ToIndentedString).
Json	Reading JSON text: see Json.Parse and JsonValue.
List<T>	A growable array.
Mutex<T>	A value that several threads share, guarded by a lock.
MutexGuard<T>	Holds the lock of a Mutex<T> until Dispose().
Process	Runs other programs and reads environment variables (static functions).
Queue<T>	A queue of values: first in, first out.
Random	Pseudo-random numbers (xorshift64*, seeded with SplitMix64).
RegexMatch	A match of a Regex: where it is, its text and the text of its groups.
Regex	Regular expressions: matching, searching, replacing and splitting text.
Stack<T>	A stack of values: last in, first out.
FileStream	A file, read and written as bytes, with seeking.
StreamReader	Reads a UTF-8 text file line by line (or all of it).
StreamWriter	Writes text to a file as UTF-8.
StringBuilder	Builds a string without copying it for every ‘+’.
Thread<T>	The handle of a running thread function that returns a T: start Square(6) runs thread int Square(int x) on its own OS thread and returns a Thread<int> right away.
DayOfWeek	The days of the week, with the numbers of .NET (Sunday is 0).
EncodingKind	The encodings that Encoding knows.
IoError	The errors of file and folder operations (File, Directory, FileStream).
ParseError	The errors of parsing numbers (String.ParseInt, String.ParseInt64, String.ParseDouble).
EncodingError	The errors of decoding bytes into text (Encoding.GetString).
JsonKind	The kind of a JsonValue.
JsonError	The errors of Json.Parse; the message says where the problem is (line and column).
RegexError	The error of Regex.Create.
SeekOrigin	Where FileStream.Seek counts from.