static CountCache()
{
var enumerableType = typeof(TEnumerable);
var enumerableParameter = Expression.Parameter(enumerableType);
var getEnumeratorInfo = enumerableType.GetMethod("GetEnumerator");
var enumeratorType = getEnumeratorInfo.ReturnType;
var moveNext = enumeratorType.GetMethod("MoveNext");
if (moveNext is null)
{
moveNext = typeof(IEnumerator).GetMethod("MoveNext");
}
var enumeratorVariable = Expression.Variable(enumeratorType);
var counterVariable = Expression.Variable(typeof(long));
var breakLabel = Expression.Label();
var body = Expression.Block(new[] { enumeratorVariable, counterVariable },
Expression.Assign(counterVariable, Expression.Constant(0L)),
Expression.Assign(enumeratorVariable, Expression.Call(enumerableParameter, getEnumeratorInfo)),
ExpressionEx.Using(enumeratorVariable,
ExpressionEx.While(
Expression.Equal(
Expression.Call(enumeratorVariable, moveNext),
Expression.Constant(true)),
Expression.Increment(counterVariable))),
counterVariable);
count = Expression.Lambda <Func <TEnumerable, long> >(body, enumerableParameter).Compile();
}
static Func <TEnumerable, int> CountCustom()
{
var enumerableParameter = Expression.Parameter(typeof(TEnumerable), "source");
var enumeratorVariable = Expression.Variable(typeof(TEnumerator), "enumerator");
var counterVariable = Expression.Variable(typeof(int), "counter");
var body = Expression.Block(new[] { enumeratorVariable, counterVariable },
Expression.Assign(counterVariable, Expression.Constant(0)),
Expression.Assign(enumeratorVariable, Expression.Call(enumerableParameter, "GetEnumerator", null)),
ExpressionEx.Using(enumeratorVariable,
ExpressionEx.While(
Expression.Call(enumeratorVariable, typeof(IEnumerator).GetMethod("MoveNext")),
Expression.Assign(counterVariable, Expression.Increment(counterVariable)))),
counterVariable);
return(Expression.Lambda <Func <TEnumerable, int> >(body, enumerableParameter).Compile());
}
static Func <IEnumerable, int> CreateCount(Type enumerableType)
{
var enumeratorType = enumerableType
.GetMethod("GetEnumerator", BindingFlags.Instance | BindingFlags.Public)
.ReturnType;
var enumerableParameter = Expression.Parameter(enumerableType, "source");
var enumeratorVariable = Expression.Variable(enumeratorType, "enumerator");
var counterVariable = Expression.Variable(typeof(int), "counter");
var body = Expression.Block(new[] { enumeratorVariable, counterVariable },
Expression.Assign(counterVariable, Expression.Constant(0)),
Expression.Assign(enumeratorVariable, Expression.Call(enumerableParameter, "GetEnumerator", null)),
ExpressionEx.Using(enumeratorVariable,
ExpressionEx.While(
Expression.Call(enumeratorVariable, typeof(IEnumerator).GetMethod("MoveNext")),
Expression.Assign(counterVariable, Expression.Increment(counterVariable)))),
counterVariable);
return(Expression.Lambda <Func <IEnumerable, int> >(body, enumerableParameter).Compile());
}
