• Patrick (5/5) Oct 20 2017 The compiler seems to reject the following code in a class method:
• Jonathan M Davis (6/9) Oct 20 2017 "this" is not a type. is(T : U) is true if T is implicitly convertible t...
• Patrick (7/23) Oct 20 2017 Thank you.
• Steven Schveighoffer (5/8) Oct 20 2017 The compiler generally doesn't "fix" errors for you, it tells you there
• Patrick (8/17) Oct 20 2017 Not asking the compiler to fix my errors.
• Steven Schveighoffer (10/24) Oct 20 2017 class C
• Patrick (10/36) Oct 20 2017 If I explicitly wrote: is(typeof(myC) : typeof(c)) the outcome
• Igor (9/52) Oct 21 2017 But with the current compiler you would never write
• Patrick (17/25) Oct 21 2017 But what value is evaluating a class type to a primitive type? It
• user1234 (9/18) Oct 20 2017 Strangely this is not always true, in other contexts this is seen
• Steven Schveighoffer (4/13) Oct 20 2017 Definitely a bug. You should have to write typeof(this) (which is valid

Patrick <tengai650 gmail.com> writes:

The compiler seems to reject the following code in a class method:

bool test = is(this : myClass);

Could some please explain this?

Thanks,

Patrick

Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:

On Friday, October 20, 2017 21:32:48 Patrick via Digitalmars-d-learn wrote:
 The compiler seems to reject the following code in a class method:

 bool test = is(this : myClass);

 Could some please explain this?

"this" is not a type. is(T : U) is true if T is implicitly convertible to U.
T and U must both be types. So, you need to use the types of this and
myClass, even if that's just is(typeof(this) : typeof(myClass)) rather than
explicitly using their types.

- Jonathan M Davis

Patrick <tengai650 gmail.com> writes:

On Friday, 20 October 2017 at 21:42:32 UTC, Jonathan M Davis 
wrote:
 On Friday, October 20, 2017 21:32:48 Patrick via 
 Digitalmars-d-learn wrote:
 The compiler seems to reject the following code in a class 
 method:

 bool test = is(this : myClass);

 Could some please explain this?

 "this" is not a type. is(T : U) is true if T is implicitly 
 convertible to U.
 T and U must both be types. So, you need to use the types of 
 this and
 myClass, even if that's just is(typeof(this) : typeof(myClass)) 
 rather than
 explicitly using their types.

 - Jonathan M Davis

Thank you.

Due to the very specific nature of the 'is' operator, why 
wouldn't the compiler know to implicitly query the class types? 
Why must it be explicitly written, typeof(this)?

Patrick

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 10/20/17 5:55 PM, Patrick wrote:
 Due to the very specific nature of the 'is' operator, why wouldn't the 
 compiler know to implicitly query the class types? Why must it be 
 explicitly written, typeof(this)?

The compiler generally doesn't "fix" errors for you, it tells you there 
is a problem, and then you have to fix it. You have to be clear and 
unambiguous to the compiler. Otherwise debugging would be hell.

-Steve

Patrick <tengai650 gmail.com> writes:

On Friday, 20 October 2017 at 22:15:36 UTC, Steven Schveighoffer 
wrote:
 On 10/20/17 5:55 PM, Patrick wrote:
 Due to the very specific nature of the 'is' operator, why 
 wouldn't the compiler know to implicitly query the class 
 types? Why must it be explicitly written, typeof(this)?

 The compiler generally doesn't "fix" errors for you, it tells 
 you there is a problem, and then you have to fix it. You have 
 to be clear and unambiguous to the compiler. Otherwise 
 debugging would be hell.

 -Steve

Not asking the compiler to fix my errors.

When would
is(this, myClass) not mean: is(typeof(this) : typeof(myClass))?

Why would "is(this, myClass)" be ambiguous? What other 
interpretation would "is(this, myClass)" imply?

Patrick

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 10/20/17 6:23 PM, Patrick wrote:
 On Friday, 20 October 2017 at 22:15:36 UTC, Steven Schveighoffer wrote:
 On 10/20/17 5:55 PM, Patrick wrote:
 Due to the very specific nature of the 'is' operator, why wouldn't 
 the compiler know to implicitly query the class types? Why must it be 
 explicitly written, typeof(this)?

 The compiler generally doesn't "fix" errors for you, it tells you 
 there is a problem, and then you have to fix it. You have to be clear 
 and unambiguous to the compiler. Otherwise debugging would be hell.

 Not asking the compiler to fix my errors.
 
 When would
 is(this, myClass) not mean: is(typeof(this) : typeof(myClass))?

class C
{
}

int c;

C myC;

is(myC : c);

oops, forgot to capitalize. But compiler says "I know, you really meant 
is(typeof(myC) : typeof(c)) -> false.

-Steve

Patrick <tengai650 gmail.com> writes:

On Friday, 20 October 2017 at 23:01:25 UTC, Steven Schveighoffer 
wrote:
 On 10/20/17 6:23 PM, Patrick wrote:
 On Friday, 20 October 2017 at 22:15:36 UTC, Steven 
 Schveighoffer wrote:
 On 10/20/17 5:55 PM, Patrick wrote:
 Due to the very specific nature of the 'is' operator, why 
 wouldn't the compiler know to implicitly query the class 
 types? Why must it be explicitly written, typeof(this)?

 The compiler generally doesn't "fix" errors for you, it tells 
 you there is a problem, and then you have to fix it. You have 
 to be clear and unambiguous to the compiler. Otherwise 
 debugging would be hell.

 Not asking the compiler to fix my errors.
 
 When would
 is(this, myClass) not mean: is(typeof(this) : typeof(myClass))?

 class C
 {
 }

 int c;

 C myC;

 is(myC : c);

 oops, forgot to capitalize. But compiler says "I know, you 
 really meant is(typeof(myC) : typeof(c)) -> false.

 -Steve

If I explicitly wrote: is(typeof(myC) : typeof(c)) the outcome 
would still be false and it would still require debugging. So 
your example demonstrates nothing other then a type-o was made. 
Try again...

In this unique case, the compiler should identify the class and 
primitive types are incompatible and should issue an error 
instead (and not return false).

Patrick

Igor <stojkovic.igor gmail.com> writes:

On Friday, 20 October 2017 at 23:24:17 UTC, Patrick wrote:
 On Friday, 20 October 2017 at 23:01:25 UTC, Steven 
 Schveighoffer wrote:
 On 10/20/17 6:23 PM, Patrick wrote:
 On Friday, 20 October 2017 at 22:15:36 UTC, Steven 
 Schveighoffer wrote:
 On 10/20/17 5:55 PM, Patrick wrote:
 Due to the very specific nature of the 'is' operator, why 
 wouldn't the compiler know to implicitly query the class 
 types? Why must it be explicitly written, typeof(this)?

 The compiler generally doesn't "fix" errors for you, it 
 tells you there is a problem, and then you have to fix it. 
 You have to be clear and unambiguous to the compiler. 
 Otherwise debugging would be hell.

 Not asking the compiler to fix my errors.
 
 When would
 is(this, myClass) not mean: is(typeof(this) : 
 typeof(myClass))?

 class C
 {
 }

 int c;

 C myC;

 is(myC : c);

 oops, forgot to capitalize. But compiler says "I know, you 
 really meant is(typeof(myC) : typeof(c)) -> false.

 -Steve

 If I explicitly wrote: is(typeof(myC) : typeof(c)) the outcome 
 would still be false and it would still require debugging. So 
 your example demonstrates nothing other then a type-o was made. 
 Try again...

 In this unique case, the compiler should identify the class and 
 primitive types are incompatible and should issue an error 
 instead (and not return false).

 Patrick

But with the current compiler you would never write

is(typeOf(myC) : typeof(c))

if in your mind "c" is actually a class "C" because if that is in 
your mind you would just write

is(typeof(myC) : c)

which would get you the error. You only need typeof(variable) to 
get to the type, there is no point in doing typeof(type), you 
just write type and C is a type. Right?

Patrick <tengai650 gmail.com> writes:

 But with the current compiler you would never write

 is(typeOf(myC) : typeof(c))

 if in your mind "c" is actually a class "C" because if that is 
 in your mind you would just write

 is(typeof(myC) : c)

 which would get you the error. You only need typeof(variable) 
 to get to the type, there is no point in doing typeof(type), 
 you just write type and C is a type. Right?

But what value is evaluating a class type to a primitive type? It 
will never be true? There has to be a reasonable chance for the 
evaulation to be true for the 'is' operator to provide value. The 
compiler should reject this 'is' statement or at minimum issue a 
warning of incompatible types. This is nonsense creep of unusable 
code (being able to write code that has no meaning and value).

This is equivalent to writing code like the following. It is just 
more obfuscated:

if(false)
{
  ...
}
else
{
  ...
}

Patrick

user1234 <user1234 12.nl> writes:

On Friday, 20 October 2017 at 21:42:32 UTC, Jonathan M Davis 
wrote:
 On Friday, October 20, 2017 21:32:48 Patrick via 
 Digitalmars-d-learn wrote:
 The compiler seems to reject the following code in a class 
 method:

 bool test = is(this : myClass);

 Could some please explain this?

 "this" is not a type.

Strangely this is not always true, in other contexts this is seen 
as atype, although probably a bug

class Foo
{
     class Bar : this {}
     static assert(is(Bar : Foo));
}

Steven Schveighoffer <schveiguy yahoo.com> writes:

On 10/20/17 7:04 PM, user1234 wrote:
 Strangely this is not always true, in other contexts this is seen as 
 atype, although probably a bug
 
 class Foo
 {
      class Bar : this {}
      static assert(is(Bar : Foo));
 }
 

Definitely a bug. You should have to write typeof(this) (which is valid 
in this context).

-Steve