ExpressionExtensions.cs

using System.Linq.Expressions;
using System.Reflection;

namespace BytecodeApi.Extensions;

/// <summary>
/// Provides a set of <see langword="static" /> methods for interaction with <see cref="Expression" /> objects.
/// </summary>
public static class ExpressionExtensions
{
	/// <summary>
	/// Returns the member name of this <see cref="Expression{TDelegate}" />. If this instance does not resolve to a <see cref="MemberExpression" />, <see langword="null" /> is returned.
	/// </summary>
	/// <typeparam name="T">The member type.</typeparam>
	/// <param name="member">The member to retrieve its name from.</param>
	/// <returns>
	/// The member name of this <see cref="Expression{TDelegate}" />, or <see langword="null" />, if this instance does not resolve to a <see cref="MemberExpression" />.
	/// </returns>
	public static string? GetMemberName<T>(this Expression<Func<T>> member)
	{
		Check.ArgumentNull(member);

		return (member.Body as MemberExpression)?.Member.Name;
	}
	/// <summary>
	/// Retrieves the value of the member of this <see cref="Expression{TDelegate}" />.
	/// </summary>
	/// <typeparam name="T">The member type.</typeparam>
	/// <param name="member">The member to retrieve its value from.</param>
	/// <returns>
	/// The value of the member of this <see cref="Expression{TDelegate}" />.
	/// </returns>
	public static T GetMemberValue<T>(this Expression<Func<T>> member)
	{
		Check.ArgumentNull(member);

		return (T)Expression.Lambda<Func<object>>(Expression.Convert((MemberExpression)member.Body, typeof(object))).Compile()();
	}
	/// <summary>
	/// Sets the value of the member of this <see cref="Expression{TDelegate}" />.
	/// </summary>
	/// <typeparam name="T">The member type.</typeparam>
	/// <param name="member">The member from which to update the value.</param>
	/// <param name="obj">The class instance of <paramref name="member" />, or <see langword="null" />, if the member is <see langword="static" />.</param>
	/// <param name="value">The new value to be assigned to <paramref name="member" />.</param>
	public static void SetMemberValue<T>(this Expression<Func<T>> member, object obj, T value)
	{
		Check.ArgumentNull(member);

		MemberInfo? memberInfo = (member.Body as MemberExpression)?.Member;

		if (memberInfo is PropertyInfo property)
		{
			property.SetValue(obj, value);
		}
		else if (memberInfo is FieldInfo field)
		{
			field.SetValue(obj, value);
		}
		else
		{
			throw Throw.UnsupportedType(nameof(member));
		}
	}
}