C# 7.0, the latest major version of the extremely popular programming language, was released in March 2017 alongside Visual Studio 2017, bringing a number of new features and capabilities to the table. Today we'll continue our deep dive into some of these awesome features in our ongoing series, What's New in C# 7.0?:
tuple types, tuple literals, and out variables.pattern matching and local functions.digit separator, binary literals, returning references and local reference variables.Today in part 4 we'll cover new expression-bodied members and throw expressions, so let's get going!
C# 6.0 introduced expression body definitions with method and property get declarations. The expression body definition syntax allows single-expression bodies to be written in a more concise and compact format. At the most basic level, an expression-bodied member looks like: member => expression;.
As of C# 6.0, expression bodies can be used for methods and property get declarations. For example, here is a basic User class that provides the Email and Name properties using expression body syntax. The same syntax is also used for the ToString() override method:
internal class User
{
private readonly string _email;
private readonly string _name;/// <summary>
/// Email property getter with expression body syntax.
/// </summary>
internal string Email => _email;
/// <summary>
/// Name property getter with expression body syntax.
/// </summary>
internal string Name => _name;internal User(string name, string email)
{
_email = email;
_name = name;
}
/// <summary>
/// Override ToString() method with expression body syntax.
/// </summary>
/// <returns>Name and email combination.</returns>
public override string ToString() => $"{Name} - {Email}";
}
C# 7.0 adds a number of new expression-bodied members to the list valid list, including constructors, finalizers, property setters, and indexers. For the first three, below we've modified our User class to include all expression-bodied members (except an indexer, since it doesn't make much sense in this context):
internal class User
{
private string _email;
private string _name;/// <summary>
/// Email property with expression body syntax.
/// </summary>
internal string Email
{
get => _email;
set => _email = value;
}/// <summary>
/// Name property with expression body syntax.
/// </summary>
internal string Name
{
get => _name;
set => _name = value;
}/// <summary>
/// Constructor with expression body syntax.
/// </summary>
/// <param name="email"></param>
internal User(string email) => _email = email;internal User(string name, string email)
{
_email = email;
_name = name;
}/// <summary>
/// Override ToString() method with expression body syntax.
/// </summary>
/// <returns>Name and email combination.</returns>
public override string ToString() => $"{Name} - {Email}";/// <summary>
/// Destructor with expression body syntax.
/// </summary>
~User() => Logging.Log($"{this} is being destroyed.");
}// <Utility>/Logging.cs
using System;
using System.Diagnostics;namespace Utility
{
/// <summary>
/// Houses all logging methods for various debug outputs.
/// </summary>
public static class Logging
{
private const char SeparatorCharacterDefault = '-';
private const int SeparatorLengthDefault = 40;/// <summary>
/// Determines type of output to be generated.
/// </summary>
public enum OutputType
{
/// <summary>
/// Default output.
/// </summary>
Default,
/// <summary>
/// Output includes timestamp prefix.
/// </summary>
Timestamp
}/// <summary>
/// Outputs to <see cref="Debug.WriteLine(String)"/>.
/// </summary>
/// <param name="value">Value to be output to log.</param>
/// <param name="outputType">Output type.</param>
public static void Log(string value, OutputType outputType = OutputType.Default)
{
Debug.WriteLine(outputType == OutputType.Timestamp
? $"[{StopwatchProxy.Instance.Stopwatch.Elapsed}] {value}"
: value);
}/// <summary>
/// When <see cref="Exception"/> parameter is passed, modifies the output to indicate
/// if <see cref="Exception"/> was expected, based on passed in `expected` parameter.
/// <para>Outputs the full <see cref="Exception"/> type and message.</para>
/// </summary>
/// <param name="exception">The <see cref="Exception"/> to output.</param>
/// <param name="expected">Boolean indicating if <see cref="Exception"/> was expected.</param>
/// <param name="outputType">Output type.</param>
public static void Log(Exception exception, bool expected = true, OutputType outputType = OutputType.Default)
{
var value = $"[{(expected ? "EXPECTED" : "UNEXPECTED")}] {exception}: {exception.Message}";Debug.WriteLine(outputType == OutputType.Timestamp
? $"[{StopwatchProxy.Instance.Stopwatch.Elapsed}] {value}"
: value);
}/// <summary>
/// Outputs to <see cref="Debug.WriteLine(Object)"/>.
///
/// ObjectDumper: http://stackoverflow.com/questions/852181/c-printing-all-properties-of-an-object&lt;/cref
/// </summary>
/// <param name="value">Value to be output to log.</param>
/// <param name="outputType">Output type.</param>
public static void Log(object value, OutputType outputType = OutputType.Default)
{
Debug.WriteLine(outputType == OutputType.Timestamp
? $"[{StopwatchProxy.Instance.Stopwatch.Elapsed}] {ObjectDumper.Dump(value)}"
: ObjectDumper.Dump(value));
}/// <summary>
/// Outputs a dashed line separator to <see cref="Debug.WriteLine(String)"/>.
/// </summary>
/// <param name="length">Total separator length.</param>
/// <param name="char">Separator character.</param>
public static void LineSeparator(int length = SeparatorLengthDefault, char @char = SeparatorCharacterDefault)
{
Debug.WriteLine(new string(@char, length));
}/// <summary>
/// Outputs a dashed line separator to <see cref="Debug.WriteLine(String)"/>,
/// with inserted text centered in the middle.
/// </summary>
/// <param name="insert">Inserted text to be centered.</param>
/// <param name="length">Total separator length.</param>
/// <param name="char">Separator character.</param>
public static void LineSeparator(string insert, int length = SeparatorLengthDefault, char @char = SeparatorCharacterDefault)
{
// Default output to insert.
var output = insert;if (insert.Length < length)
{
// Update length based on insert length, less a space for margin.
length -= insert.Length + 2;
// Halve the length and floor left side.
var left = (int) Math.Floor((decimal) (length / 2));
var right = left;
// If odd number, add dropped remainder to right side.
if (length % 2 != 0) right += 1;// Surround insert with separators.
output = $"{new string(@char, left)} {insert} {new string(@char, right)}";
}
// Output.
Debug.WriteLine(output);
}
}
}
We also have a UserCollection class that contains a private User[] _users property:
internal class UserCollection
{
private readonly User[] _users =
{
new User("Alice Smith", "alice.smith@airbrake.io"),
new User("Bob Smith", "bob.smith@airbrake.io"),
new User("Christine Parker", "christine.parker@airbrake.io"),
new User("Danny Danson", "danny.danson@airbrake.io")
};
/// <summary>
/// Indexer with get/set expression body syntax.
/// </summary>
/// <param name="index">Index of User.</param>
/// <returns>User.</returns>
public User this[int index]
{
get => _users[index];
set => _users[index] = value;
}
}
We can then instantiate a new UserCollection instance, use the indexer to retrieve the second User element, and then output the returned value to the console (using the ToString() override method we defined earlier):
class Program
{
static void Main(string[] args)
{
var users = new UserCollection();
Logging.Log(users[1].ToString());
// Bob Smith - bob.smith@airbrake.io
}
}
Closely related to expression-bodied members, C# 7.0 also introduces the ability to create throw expressions. In many places where an expression might be valid, a throw expression can be used to directly throw an Exception. For example, here we're causing attempts to use the setter of the User.Email property to throw a new NotImplementedException:
internal class User
{
private string _email;
private string _name;/// <summary>
/// Email property with expression body syntax
/// getter and throw expression for setter.
/// </summary>
internal string Email
{
get => _email;
set => throw new NotImplementedException("User.Email.set is not implemented.");
}
// ...
}
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