Apparent inconsistency in definitions of structural types

> The compiler seems to prefer methods defined with "()" ending, when
> structural types are defined, giving it one method without is
> tolerated, more than one will get
> it upset. Is this a bug ?

Seems to be a bit more complicated than that:

scala> type Z = { def isEmpty:Boolean }
defined type alias Z

scala> "":Z
res3: Z =

scala> type Z = { def trim: String }
defined type alias Z

scala> "":Z
:9: error: type mismatch;
found : java.lang.String("")
required: Z
"":Z
^

In structural types, methods without parameter lists are different
than methods with one empty parameter list.

What is happening here, I'd wager, is that String defines isEmpty(),
while WrappedString defines isEmpty, so the latter is available
through implicit conversion.

The same is not true for trim().

People (including Paul Phillips) have asked before for these two being
considered equal, but Odersky was pretty firm in that this cannot be
allowed.

2011/12/14 Maxime Lévesque :
>
> The compiler seems to prefer methods defined with "()" ending, when
> structural types are defined, giving it one method without is tolerated,
> more than one will get
> it upset. Is this a bug ?
>
>
> The following snipets compile :
> ====================================================================
> scala>   type Z = { def isEmpty(): Boolean; def trim(): String}
> defined type alias Z
>
> scala>   "" : Z
> res2: Z = ""
>
> scala>   type Z = { def isEmpty: Boolean}
> defined type alias Z
>
> scala>   "" : Z
> res3: Z =
> ====================================================================
>
>
> The following don't :
>
> ====================================================================
> scala>   type Z = { def isEmpty(): Boolean;  def trim: String }
> defined type alias Z
>
> scala>   "" : Z
> :9: error: type mismatch;
>  found   : java.lang.String("")
>  required: Z
>                 "" : Z
>                 ^
>
>
> scala>   type Z = { def isEmpty(): Boolean; def trim: String}
> defined type alias Z
>
> scala>   "" : Z
> :9: error: type mismatch;
>  found   : java.lang.String("")
>  required: Z
>                 "" : Z
>                 ^
> ====================================================================
>
>

In structural types, methods without parameter lists are different
than methods with one empty parameter list.

What is happening here, I'd wager, is that String defines isEmpty(),
while WrappedString defines isEmpty, so the latter is available
through implicit conversion.

The same is not true for trim().

People (including Paul Phillips) have asked before for these two being
considered equal, but Odersky was pretty firm in that this cannot be
allowed.

2011/12/14 Maxime Lévesque <maxime.levesque@gmail.com>:
>
> The compiler seems to prefer methods defined with "()" ending, when
> structural types are defined, giving it one method without is tolerated,
> more than one will get
> it upset. Is this a bug ?
>
>
> The following snipets compile :
> ====================================================================
> scala>   type Z = { def isEmpty(): Boolean; def trim(): String}
> defined type alias Z
>
> scala>   "" : Z
> res2: Z = ""
>
> scala>   type Z = { def isEmpty: Boolean}
> defined type alias Z
>
> scala>   "" : Z
> res3: Z =
> ====================================================================
>
>
> The following don't :
>
> ====================================================================
> scala>   type Z = { def isEmpty(): Boolean;  def trim: String }
> defined type alias Z
>
> scala>   "" : Z
> <console>:9: error: type mismatch;
>  found   : java.lang.String("")
>  required: Z
>                 "" : Z
>                 ^
>
>
> scala>   type Z = { def isEmpty(): Boolean; def trim: String}
> defined type alias Z
>
> scala>   "" : Z
> <console>:9: error: type mismatch;
>  found   : java.lang.String("")
>  required: Z
>                 "" : Z
>                 ^
> ====================================================================
>
>



--
Daniel C. Sobral

I travel to the future all the time.