private static Expression <T> Compose <T>(this Expression <T> first, Expression <T> second,
Func <Expression, Expression, Expression> merge)
{
var map = first.Parameters
.Select((f, i) => new { f, s = second.Parameters[i] })
.ToDictionary(p => p.s, p => p.f);
var secondBody = ParameterReBinder.ReplaceParameters(map, second.Body);
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
/// <summary>
/// Combines the first expression with the second using the specified merge function.
/// </summary>
static Expression <T> Compose <T>(this Expression <T> first, Expression <T> second,
Func <Expression, Expression, Expression> merge)
{
// zip parameters (map from parameters of second to parameters of first)
var map = first.Parameters
.Select((f, i) => new { f, s = second.Parameters[i] })
.ToDictionary(p => p.s, p => p.f);
// replace parameters in the second lambda expression with the parameters in the first
var secondBody = ParameterReBinder.ReplaceParameters(map, second.Body);
// create a merged lambda expression with parameters from the first expression
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
internal static Expression <T> Compose <T>(
this Expression <T> first,
Expression <T> second,
Func <Expression, Expression, Expression> merge)
{
Dictionary <ParameterExpression, ParameterExpression> map =
first.Parameters
.Select((parameter, index) => (parameter, second: second.Parameters[index]))
.ToDictionary(p => p.second, p => p.parameter);
Expression secondBody = ParameterReBinder.ReplaceParameters(map, second.Body);
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}