Expression3.cs

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using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Dynamic.Utils;
 
namespace System.Linq.Expressions;
 
internal sealed class Expression3<TDelegate> : Expression<TDelegate>
{
    private object _par0;
 
    private readonly ParameterExpression _par1;
 
    private readonly ParameterExpression _par2;
 
    internal override int ParameterCount => 3;
 
    public Expression3(Expression body, ParameterExpression par0, ParameterExpression par1, ParameterExpression par2)
        : base(body)
    {
        _par0 = par0;
        _par1 = par1;
        _par2 = par2;
    }
 
    internal override ParameterExpression GetParameter(int index)
    {
        return index switch
        {
            0 => ExpressionUtils.ReturnObject<ParameterExpression>(_par0), 
            1 => _par1, 
            2 => _par2, 
            _ => throw Error.ArgumentOutOfRange("index"), 
        };
    }
 
    internal override bool SameParameters(ICollection<ParameterExpression> parameters)
    {
        if (parameters != null && parameters.Count == 3)
        {
            if (_par0 is ReadOnlyCollection<ParameterExpression> current)
            {
                return ExpressionUtils.SameElements(parameters, current);
            }
            using IEnumerator<ParameterExpression> enumerator = parameters.GetEnumerator();
            enumerator.MoveNext();
            if (enumerator.Current == _par0)
            {
                enumerator.MoveNext();
                if (enumerator.Current == _par1)
                {
                    enumerator.MoveNext();
                    return enumerator.Current == _par2;
                }
            }
        }
        return false;
    }
 
    internal override ReadOnlyCollection<ParameterExpression> GetOrMakeParameters()
    {
        return ExpressionUtils.ReturnReadOnly(this, ref _par0);
    }
 
    internal override Expression<TDelegate> Rewrite(Expression body, ParameterExpression[] parameters)
    {
        if (parameters != null)
        {
            return Expression.Lambda<TDelegate>(body, parameters);
        }
        return Expression.Lambda<TDelegate>(body, new ParameterExpression[3]
        {
            ExpressionUtils.ReturnObject<ParameterExpression>(_par0),
            _par1,
            _par2
        });
    }
}