public static Expression <Func <TSource, TResult> > Continue <TSource, TItem, TResult>(this Expression <Func <TSource, TItem> > sourceExpression, Expression <Func <TItem, TResult> > continueExpression)
{
ExpressionVisitor rebinder;
switch (sourceExpression.Body.NodeType)
{
case ExpressionType.MemberAccess:
{
rebinder = new MemberRebinder(continueExpression.Parameters[0], (MemberExpression)sourceExpression.Body);
break;
}
case ExpressionType.Parameter:
{
rebinder = new ParameterRebinder(continueExpression.Parameters[0], (ParameterExpression)sourceExpression.Body);
break;
}
default:
rebinder = new ExpressionRebinder(continueExpression.Parameters[0], sourceExpression.Body);
break;
}
Expression resultBody = rebinder.Visit(continueExpression.Body);
return(Expression.Lambda <Func <TSource, TResult> >(resultBody, sourceExpression.Parameters));
}
/// <summary>组合两个表达式</summary>
public 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)
// replace parameters in the second lambda expression with parameters from the first
// apply composition of lambda expression bodies to parameters from the first expression
var map = first.Parameters.Select((f, i) => new { f, s = second.Parameters[i] }).ToDictionary(p => p.s, p => p.f);
var secondBody = ExpressionRebinder.ReplaceParameters(map, second.Body);
return(Expression.Lambda <T>(merge(first.Body, secondBody), first.Parameters));
}
public static Expression Continue(this Expression sourceBody, Expression continueBody, ParameterExpression continueParameter)
{
var rebinder = new ExpressionRebinder(continueParameter, sourceBody);
return(rebinder.Visit(continueBody));
}
