I agree with you analysis. The primary problem is we cannot know the length
of the list before runtime thus we cannot write a for loop before runtime.
The right way will be what you have suggested, to write a for statement
directly and generate code from there.
Thanks,
Rui
On Mon, Dec 30, 2019 at 10:30 PM Feng Zhu <wellfeng...@gmail.com> wrote:
> >
> > As you can see, I know "myFunc" returns a list, so I want to make each
> > element of that list an expression so I can continue manipulating them.
> > Eventually they will be used to generate code.
> >
>
> AFAIK, it is nearly impossible know the list's length if we do not rely on
> "evaluate", because it is determined in runtime.
> Therefore, the (*List<Expression>*) may be difficult.
> But if you want to manipulate the list element in code, I think we can also
> use the functions provided in Expressions.
>
> * // org.apache.calcite.runtime.SqlFunctions.myFunc()*
> MethodCallExpression mce = Expressions.call(SqlFunctions.class,
> "myFunc");
> * // final java.util.List res*
> ParameterExpression pe = Expressions.parameter(mce.type, "res");
> * // final java.util.List res =
> org.apache.calcite.runtime.SqlFunctions.myFunc();*
> DeclarationStatement statement = Expressions.declare(Modifier.FINAL,
> pe, mce);
> System.out.println(statement);
>
> ParameterExpression pe1 = Expressions.parameter(Object.class, "obj");
> Expression input = Expressions.convert_(pe1, Long.class);
> MethodCallExpression mce2 = Expressions.call(SqlFunctions.class,
> "myFunc2", input);
> org.apache.calcite.linq4j.tree.Statement s =
> Expressions.statement(mce2);
>
>
>
> * //for (Object obj : res) { //
> org.apache.calcite.runtime.SqlFunctions.myFunc2((Long) obj); //}*
> ForEachStatement forEachStatement = Expressions.forEach(pe1, pe, s);
>
>
> Best,
> Feng
>
> Rui Wang <amaliu...@apache.org> 于2019年12月31日周二 下午1:42写道：
>
> > Thanks Feng.
> >
> > I want to access elements before evaluation. Use your example:
> >
> > Define:
> > public static List<Long> myFunc() { return Arrays.asList(1L, 2L); }
> > public static Long myFunc2(Long i) { return i - 1l }
> >
> > I want build expressions as the following:
> >
> > List<Expression> ret = new ArrayList();
> > MethodCallExpression mce = Expressions.call(SqlFunctions.class,"myFunc");
> >
> > // how to make each element an expression?
> > for (Expression expr : mce) {
> > ret.dd(Expressions.call(SqlFunctions.class, "myFunc2", expr));
> > }
> >
> > return ret;
> >
> >
> >
> > As you can see, I know "myFunc" returns a list, so I want to make each
> > element of that list an expression so I can continue manipulating them.
> > Eventually they will be used to generate code.
> >
> >
> >
> > -Rui
> >
> >
> >
> >
> >
> >
> > On Mon, Dec 30, 2019 at 9:29 PM Feng Zhu <wellfeng...@gmail.com> wrote:
> >
> > > >
> > > > Basically I know the function return a list so I want to access each
> > > > element of it. Ideally I can get a List<Expression> ret =
> > > > Expressions.call(FindMethod("myFunc"))
> > > >
> > > Can you elaborate on what do you want? i.e., *List<Expression> ret*
> > > If you want to get the element of a method call result, you can
> evaluate
> > > the expression and cast it to list.
> > >
> > > For example, assume "myFunc" in SqlFunctions.
> > >
> > >
> > >
> > > * public static List<Long> myFunc() { return Arrays.asList(1L, 2L);
> > }*
> > >
> > >
> > > * MethodCallExpression mce = Expressions.call(SqlFunctions.class,
> > > "myFunc"); List<Long> ret = (List<Long>) Expressions.evaluate(mce);*
> > >
> > > Best,
> > >
> > > Rui Wang <amaliu...@apache.org> 于2019年12月31日周二 下午12:14写道：
> > >
> > > > Hi community,
> > > >
> > > > Let's say I define a function like this:
> > > >
> > > > List<Long> myFunc() {
> > > > // function body
> > > > // do something
> > > > // return a list of long
> > > > }
> > > >
> > > > Then by linq4j library, I can
> > > >
> > > > Expression ret = Expressions.call(
> > > > FindMethod("myFunc")
> > > > )
> > > >
> > > >
> > > > my question is, how to make the returned expression of the call to
> be a
> > > > list, or something equivalent?
> > > >
> > > > Basically I know the function return a list so I want to access each
> > > > element of it. Ideally I can get a List<Expression> ret =
> > > > Expressions.call(FindMethod("myFunc"))
> > > >
> > > >
> > > > -Rui
> > > >
> > >
> >
>
