Rename .project to .project.SAMPLE #65
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This should have been done a long time ago, when .classpath was renamed to .classpath.SAMPLE. Both files are needed to import the scala compiler in Eclipse, and having just one guarantees a broken project.
paulp
added a commit
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Dec 21, 2011
Rename .project to .project.SAMPLE
olafurpg
added a commit
to olafurpg/scala
that referenced
this pull request
Jul 17, 2018
This commit uncomments the disabled `productElementName` method.
The benefit of this change is that it becomes possible to pretty-print
`Product` instances with field, for example
```scala
case class User(name: String, age: Int)
def pretty(p: Product): String =
p.productElementNames.zip(p.productIterator)
.map { case (name, value) => s"$name=$value" }
.mkString(p.productPrefix + "(", ", ", ")")
toPrettyProduct(User("Susan", 42))
// res0: String = User(name=Susan, age=42)
```
The downside of this change is that it produces more bytecode for each
case-class definition. I am not versed enough in reading javap output
to determine the exact bytecode size for a given method. I tried the
following:
```scala
> case class A(a: Int, b: Int, c: Int)
> :javap -c A
public java.lang.String productElementName(int);
Code:
0: iload_1
1: istore_2
2: iload_2
3: tableswitch { // 0 to 2
0: 28
1: 33
2: 38
default: 43
}
28: ldc scala#78 // String a
30: goto 58
33: ldc scala#79 // String b
35: goto 58
38: ldc scala#80 // String c
40: goto 58
43: new scala#67 // class java/lang/IndexOutOfBoundsException
46: dup
47: iload_1
48: invokestatic scala#65 // Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
51: invokevirtual scala#70 // Method java/lang/Object.toString:()Ljava/lang/String;
54: invokespecial scala#73 // Method java/lang/IndexOutOfBoundsException."<init>":(Ljava/lang/String;)V
57: athrow
58: areturn
```
olafurpg
added a commit
to olafurpg/scala
that referenced
this pull request
Jul 17, 2018
This commit uncomments the disabled `productElementName` method.
The benefit of this change is that it becomes possible to pretty-print
`Product` instances with field, for example
```scala
case class User(name: String, age: Int)
def pretty(p: Product): String =
p.productElementNames.zip(p.productIterator)
.map { case (name, value) => s"$name=$value" }
.mkString(p.productPrefix + "(", ", ", ")")
toPrettyProduct(User("Susan", 42))
// res0: String = User(name=Susan, age=42)
```
The downside of this change is that it produces more bytecode for each
case-class definition. I am not versed enough in reading javap output
to determine the exact bytecode size for a given method. I tried the
following:
```scala
> case class A(a: Int, b: Int, c: Int)
> :javap -c A
public java.lang.String productElementName(int);
Code:
0: iload_1
1: istore_2
2: iload_2
3: tableswitch { // 0 to 2
0: 28
1: 33
2: 38
default: 43
}
28: ldc scala#78 // String a
30: goto 58
33: ldc scala#79 // String b
35: goto 58
38: ldc scala#80 // String c
40: goto 58
43: new scala#67 // class java/lang/IndexOutOfBoundsException
46: dup
47: iload_1
48: invokestatic scala#65 // Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
51: invokevirtual scala#70 // Method java/lang/Object.toString:()Ljava/lang/String;
54: invokespecial scala#73 // Method java/lang/IndexOutOfBoundsException."<init>":(Ljava/lang/String;)V
57: athrow
58: areturn
```
olafurpg
added a commit
to olafurpg/scala
that referenced
this pull request
Jul 18, 2018
This commit uncomments the disabled `productElementName` method.
The benefit of this change is that it becomes possible to pretty-print
`Product` instances with field, for example
```scala
case class User(name: String, age: Int)
def pretty(p: Product): String =
p.productElementNames.zip(p.productIterator)
.map { case (name, value) => s"$name=$value" }
.mkString(p.productPrefix + "(", ", ", ")")
toPrettyProduct(User("Susan", 42))
// res0: String = User(name=Susan, age=42)
```
The downside of this change is that it produces more bytecode for each
case-class definition. Running `:javacp -c` for a case class with three
fields yields the following results
```scala
> case class A(a: Int, b: Int, c: Int)
> :javap -c A
public java.lang.String productElementName(int);
Code:
0: iload_1
1: istore_2
2: iload_2
3: tableswitch { // 0 to 2
0: 28
1: 33
2: 38
default: 43
}
28: ldc scala#78 // String a
30: goto 58
33: ldc scala#79 // String b
35: goto 58
38: ldc scala#80 // String c
40: goto 58
43: new scala#67 // class java/lang/IndexOutOfBoundsException
46: dup
47: iload_1
48: invokestatic scala#65 // Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
51: invokevirtual scala#70 // Method java/lang/Object.toString:()Ljava/lang/String;
54: invokespecial scala#73 // Method java/lang/IndexOutOfBoundsException."<init>":(Ljava/lang/String;)V
57: athrow
58: areturn
```
Thanks to Adriaan's help, the estimated cost per `productElementName`
appears to be fixed 56 bytes and then 10 bytes for each field with
the following breakdown:
* 3 bytes for the
[string info](https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4.3)
(the actual characters are already in the constant pool)
* 4 bytes for the tableswitch entry
* 2 bytes for the ldc to load the string
* 1 byte for areturn
In my opinion, the bytecode cost is acceptably low thanks to the fact
that field name literals are already available in the constant pool.
olafurpg
added a commit
to olafurpg/scala
that referenced
this pull request
Jul 18, 2018
This commit adds two methods to the `scala.Product` trait:
```scala
trait Product {
/** Returns the field name of element at index n */
def productElementName(n: Int): String
/** Returns field names of this product. Must have same length as productIterator */
def productElementNames: Iterator[String]
}
```
Both methods have a default implementation which returns the empty
string for all field names.
This commit then changes the code-generation for case classes to
synthesize a `productElementName` method with actual class field names.
The benefit of this change is that it becomes possible to pretty-print
case classes with field names, for example
```scala
case class User(name: String, age: Int)
def toPrettyString(p: Product): String =
p.productElementNames.zip(p.productIterator)
.map { case (name, value) => s"$name=$value" }
.mkString(p.productPrefix + "(", ", ", ")")
toPrettyString(User("Susan", 42))
// res0: String = User(name=Susan, age=42)
```
The downside of this change is that it produces more bytecode for each
case-class definition. Running `:javacp -c` for a case class with three
fields yields the following results
```scala
> case class A(a: Int, b: Int, c: Int)
> :javap -c A
public java.lang.String productElementName(int);
Code:
0: iload_1
1: istore_2
2: iload_2
3: tableswitch { // 0 to 2
0: 28
1: 33
2: 38
default: 43
}
28: ldc scala#78 // String a
30: goto 58
33: ldc scala#79 // String b
35: goto 58
38: ldc scala#80 // String c
40: goto 58
43: new scala#67 // class java/lang/IndexOutOfBoundsException
46: dup
47: iload_1
48: invokestatic scala#65 // Method scala/runtime/BoxesRunTime.boxToInteger:(I)Ljava/lang/Integer;
51: invokevirtual scala#70 // Method java/lang/Object.toString:()Ljava/lang/String;
54: invokespecial scala#73 // Method java/lang/IndexOutOfBoundsException."<init>":(Ljava/lang/String;)V
57: athrow
58: areturn
```
Thanks to Adriaan's help, the estimated cost per `productElementName`
appears to be fixed 56 bytes and then 10 bytes for each field with
the following breakdown:
* 3 bytes for the
[string info](https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.4.3)
(the actual characters are already in the constant pool)
* 4 bytes for the tableswitch entry
* 2 bytes for the ldc to load the string
* 1 byte for areturn
In my opinion, the bytecode cost is acceptably low thanks to the fact
that field name literals are already available in the constant pool.
da-liii
pushed a commit
to da-liii/scala
that referenced
this pull request
Nov 11, 2018
add missing deps to kdevplatform
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This should have been done a long time ago, when .classpath was renamed to .classpath.SAMPLE. Both files are needed to import the scala compiler in Eclipse, and having just one guarantees a broken project.