BlockBuilder is fairly good at detecting constants, for example (short) 10, code generating clients (for example optiq) will generate things like "Sales department".trim(). BlockBuilder should optimize such expressions, storing them in constant members (aka static final).

We already have a notion that literals (e.g. 1 and null) are constant, and which operators modify their lvalue (see ExpressionType.modifiesLvalue). I think we'd need a notion of which classes are constant (int.class, Integer.class, String.class, Timestamp.class, ImmutableMap.class, but not AtomicInteger.class, BigDecimal.class or Map.class) and of methods that always produce the same result given the same arguments ('same' according to Objects.equals), for example String.trim but not System.currentTimeMillis or Random.nextInt.

BlockBuilder should have a built-in list of immutable classes and deterministic methods, but clients of BlockBuilder should be able to add new ones to any given instance.

And of course any expression that is a constant member is also regarded as constant. (But beware cyclic initialization.)

With this knowledge, a BlockBuilder should be able to deduce bottom-up which expressions are constant and assign them to constant members.

Hello. I've downloaded your project but stuck with build it. I am using Java SE6 and cannot build it. So, how is it possible to use this project without having to install Java 7 ?

mvn javadoc:javadoc fails under JDK1.8. Over 100 errors. Here are a few:

[ERROR] src/main/java/net/hydromatic/linq4j/ExtendedEnumerable.java:791: error: unknown tag: TSource
[ERROR] * EqualityComparer<TSource>.
[ERROR] ^
[ERROR] src/main/java/net/hydromatic/linq4j/ExtendedEnumerable.java:937: error: malformed HTML
[ERROR] * Creates a Dictionary<TKey, TValue> from an
[ERROR] ^
[ERROR] src/main/java/net/hydromatic/linq4j/ExtendedEnumerable.java:937: error: bad use of '>'
[ERROR] * Creates a Dictionary<TKey, TValue> from an
[ERROR] ^

I'd really love to play with it, but looks like it's not available on Maven. Is it?

Here's the exception when trying to print such an expression

Caused by: java.lang.IndexOutOfBoundsException: Index: 3, Size: 3
    at java.util.ArrayList.rangeCheck(ArrayList.java:604)
    at java.util.ArrayList.get(ArrayList.java:382)
    at net.hydromatic.linq4j.expressions.ConditionalStatement.accept0(ConditionalStatement.java:55)

This might be a fix:

  void accept0(ExpressionWriter writer) {
    int ifBranches = expressionList.size();
    ifBranches -= ifBranches & 1;
    for (int i = 0; i < ifBranches; i += 2) {

I am using linq4j. I am only sorting by one property and would like to sort by multiple property. If is is not supported in linq4j than what other method I can use. Following is my code snippet,

import java.util.Arrays;
import java.util.List; 
import net.hydromatic.linq4j.Linq4j;
import net.hydromatic.linq4j.function.*;

public class Linq4jExample {
 public static class Employee {
 public final int empno;
 public final String name;
 public final int deptno;

public Employee(int empno, String name, int deptno) {
  this.empno = empno;
  this.name = name;
  this.deptno = deptno;
}

public String toString() {
  return "Employee(empno: " + empno +",name: " + name + ", deptno:" + deptno    + ")";
 }
 }

public static final Employee[] emps = {
  new Employee(100, "Fred", 10),
  new Employee(110, "Bill", 30),
  new Employee(120,  "Bill", 10),
  new Employee(120, "Eric", 12),
  new Employee(130, "Janet", 13),
};

public static final Function1<Employee, Integer> EMP_DEPTNO_SELECTOR =
  new Function1<Employee, Integer>() {
    public Integer apply(Employee employee) {
      return employee.deptno;
    }
     };

public static void main(String[] args) {

  List<Employee> filter=Linq4j.asEnumerable(Arrays.asList(emps)) 
            .orderBy(new Function1<Employee,String>()
        { 
        public String apply(Employee arg0)
        {
            return arg0.name;
        }

    }).toList();

  }
 }

A potential use case could be sorting by department number and then by name.

Summary

WIndows has trouble with newlines and I'm not sure how you want to proceed.

Failure

When I run JfrSchemaFactoryTest.canRunSimpleSelectFromClassLoad on Windows, it fails on column 2 because the newlines are different:

assertThat(rs.getString(2)).isEqualTo("""
        {
          classLoader = null
          name = "java/lang/Throwable"
          package = {
            name = "java/lang"
            module = {
              name = "java.base"
              version = "17"
              location = "jrt:/java.base"
              classLoader = null
            }
            exported = true
          }
          modifiers = 33
          hidden = false
        }
        """);

Cause

JfrSchema.getConverter is using the following converter:

else if (field.getTypeName().equals("java.lang.Class")) {
    LOGGER.log(INFO, "| -> java.lang.Class");
    return event -> event.getClass(field.getName());
}

I believe when the testcase calls rs.getString(), this is calling RecordedClass.toString() which ultimately uses StructuredWriter.lineSeparator which is initialized to String.format("%n"), and this differs by platform.

Possible solutions

Should we return the java.lang.Class in this case, rather than the RecordedClass object? The Class.toString() method should produce the same result on all platforms.

Linq4j BlockBuilder incorrectly inlines a variable that might be assigned more than once along a code path. For example, in

long x = 0;
final long y = System.currentTimeMillis();
if (System.nanoTime() > 0L) {
  x = y;
}

it incorrectly inlines x, to yield

if (System.nanoTime() > 0L) {
  System.currentTimeMillis();
}

The fix is to only inline variables that are marked 'final'. The java compiler will ensure that they cannot be assigned more than once (by any code path) and cannot be read before they have been initialized.

This change may break code that relies on Linq4j inlining effectively final (but not explicitly final) variables.