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How does the compiler recognise Nullable<T> to be a 'special type'?


How does the compiler recognise Nullable<T> to be a 'special type'?

By : Dale M.
Date : November 22 2020, 12:01 PM
hope this fix your issue Based off of the Shared Source CLI 2.0, Nullable is made "special" via the PREDEFTYPEDEF macro, which takes the name "System.Nullable" and maps it to the attribute PT_G_OPTIONAL which is checked throughout the rest of the compiler.
With regards to the aliases of int → System.Int32 et al., see the "nice name" column.
code :
//         id            full type name       required  simple     numer    AggKind  fund type   elementtype,      nice name,    zero, quasi simple numer, attribute arg size serialization type,  predef attribute, arity, in mscorlib)
PREDEFTYPEDEF(PT_BYTE,   "System.Byte",         1,            1,      1,     Struct,   FT_U1,   ELEMENT_TYPE_U1,      L"byte",      0,                 0,      1,      SERIALIZATION_TYPE_U1,      PA_COUNT, 0, 1)
PREDEFTYPEDEF(PT_SHORT,  "System.Int16",        1,            1,      1,     Struct,   FT_I2,   ELEMENT_TYPE_I2,      L"short",     0,                 0,      2,      SERIALIZATION_TYPE_I2,      PA_COUNT, 0, 1)
PREDEFTYPEDEF(PT_INT,    "System.Int32",        1,            1,      1,     Struct,   FT_I4,   ELEMENT_TYPE_I4,      L"int",       0,                 0,      4,      SERIALIZATION_TYPE_I4,      PA_COUNT, 0, 1)
PREDEFTYPEDEF(PT_LONG,   "System.Int64",        1,            1,      1,     Struct,   FT_I8,   ELEMENT_TYPE_I8,      L"long",      &longZero,         0,      8,      SERIALIZATION_TYPE_I8,      PA_COUNT, 0, 1)
// ... snip ...
// Nullable<T>
PREDEFTYPEDEF(PT_G_OPTIONAL, "System.Nullable",  0,     0,     0,   Struct,   FT_STRUCT,  ELEMENT_TYPE_END,      NULL,          0,                 0,      0,      0,                          PA_COUNT, 1, 1)
/***************************************************************************************************
    Return true iff the method is the nullable ctor taking one parameter.
***************************************************************************************************/
bool FUNCBREC::IsNubCtor(METHSYM * meth)
{
    return meth && meth->getClass()->isPredefAgg(PT_G_OPTIONAL) && meth->params->size == 1 &&
        meth->params->Item(0)->isTYVARSYM() && meth->isCtor();
}


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Function to accept nullable type and return nullable type or string

Function to accept nullable type and return nullable type or string


By : itsu
Date : March 29 2020, 07:55 AM
wish of those help Basically I want to be able to have one function that takes in a Nullable Type and then returns the value if it has one or the string value "NULL" if it's null so the function needs to be able to take in any nullable type and then return that type or return the string NULL. Below is kind of what I'm looking for as an example I just can't seem to figure out what I need to do as far as my function.
code :
static string MyFunction<T>(Nullable<T> arg) where T : struct
{
    String strNULL = "NULL";

    if (arg.HasValue)
        return arg.Value.ToString();
    else
        return strNULL;
}
Recoding printf; error in .h file: compiler doesn't recognise the va_list type

Recoding printf; error in .h file: compiler doesn't recognise the va_list type


By : Jack Sun
Date : March 29 2020, 07:55 AM
hope this fix your issue If you are creating all of your own definitions, including va_list, then I assume the definition(s) you created in your .h looked at least similar to:
code :
#ifndef _VA_LIST_DEFINED
#ifdef _M_CEE_PURE
typedef System::ArgIterator va_list;
#else
typedef char *  va_list;
#endif
#define _VA_LIST_DEFINED
#endif  
#include <stdarg.h>

void variadic_function(int Param, ...) 
{
    int dslot;
    va_list params;
    va_start(params, Param);
    dslot = va_arg(params, int);
    va_end(args);
}  
Why does my java compiler not recognise so many symbols?

Why does my java compiler not recognise so many symbols?


By : Cambo
Date : March 29 2020, 07:55 AM
Does that help The documentation says that it's spelled drawString, with an uppercase S. Java is case sensitive.
What special rules does the scala compiler have for the unit type within the type system

What special rules does the scala compiler have for the unit type within the type system


By : serhat ocal
Date : March 29 2020, 07:55 AM
around this issue I'm going to answer the title question for more coverage. Unit gets special treatment in a few places, more than what's going on in those code examples. In part, this is because Unit is a figment of the compiler that reduces to void on the JVM.
code :
def foo3(): Unit = "foo"
def foo3(): Unit = { "foo" ; () }
def foo: Future[Unit] = save(customer1).map(_ => save(customer2))
def foo: Future[Unit] = save(customer1).map(_ => { save(customer2); () })
scala> val x = { }
x: Unit = ()
scala> ().==(())
<console>:12: warning: comparing values of types Unit and Unit using `==' will always yield true
       ().==(())
            ^
res2: Boolean = true
object Test {
  val a = "a".asInstanceOf[Unit]
  val b = a
}
object Test extends Object {
  def <init>(): Test.type = {
    Test.super.<init>();
    ()
  };
  private[this] val a: scala.runtime.BoxedUnit = scala.runtime.BoxedUnit.UNIT;
  <stable> <accessor> def a(): Unit = ();
  private[this] val b: scala.runtime.BoxedUnit = scala.runtime.BoxedUnit.UNIT;
  <stable> <accessor> def b(): Unit = ()
}
Compiler can't recognise setOnClickListener(....);

Compiler can't recognise setOnClickListener(....);


By : user3487884
Date : March 29 2020, 07:55 AM
This might help you Your code is returning an error because you placed actionable code outside a method. If you look closely, you'd see that the line generating the error is not enclosed inside any method.
With the exception of variable declarations and assignment, actions are meant to be enclosed inside methods. Therefore, having a setOnClickListener call which is not enclosed in any method would obviously not work. Simply move these two lines inside your onCreate() method and everything would be fine. Here's an illustration:
code :
...

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

     Button rollButton = findViewById(R.id.blahblah);
     rollButton.setOnClickListener(new View.OnClickListener());
}

...
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