internal static Expression <T> Compose <T>(this Expression <T> first, Expression <T> second, Func <Expression, Expression, Expression> merge) { // build parameter 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 parameters from // the first var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body); // apply composition of lambda expression bodies to parameters from // the first expression return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters)); }
/// <summary> /// Combines the first expression with the second using the specified merge function. /// </summary> private 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) Dictionary <ParameterExpression, ParameterExpression> map = first.Parameters .Select((x, i) => new { f = x, s = second.Parameters[i] }) .ToDictionary(y => y.s, p => p.f); // Replace parameters in the second lambda expression with the parameters in the first Expression 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)); }