Removed dummy parametr in `type_id` method.

Closes #17
Now call like:
`let id = <CFBoolean as TCFType<_>>::type_id();`

[breaking-change]

src/array.rs

@@ -104,7 +104,7 @@ impl TCFType<CFArrayRef> for CFArray {
     }
 
     #[inline]
-    fn type_id(_: Option<CFArray>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFArrayGetTypeID()
         }

src/base.rs

@@ -106,10 +106,7 @@ pub trait TCFType<ConcreteTypeRef> {
     unsafe fn wrap_under_create_rule(obj: ConcreteTypeRef) -> Self;
 
     /// Returns the type ID for this class.
-    ///
-    /// FIXME(pcwalton): The dummy parameter is there to work around the current inexpressivity of
-    /// the Rust language.
-    fn type_id(dummy: Option<Self>) -> CFTypeID;
+    fn type_id() -> CFTypeID;
 
     /// Returns the object as a wrapped `CFType`. The reference count is incremented by one.
     #[inline]
@@ -153,8 +150,7 @@ pub trait TCFType<ConcreteTypeRef> {
     /// Returns true if this value is an instance of another type.
     #[inline]
     fn instance_of<OtherConcreteTypeRef,OtherCFType:TCFType<OtherConcreteTypeRef>>(&self) -> bool {
-        let dummy: Option<OtherCFType> = None;
-        self.type_of() == TCFType::type_id(dummy)
+        self.type_of() == <OtherCFType as TCFType<_>>::type_id()
     }
 }
 
@@ -183,7 +179,7 @@ impl TCFType<CFTypeRef> for CFType {
     }
 
     #[inline]
-    fn type_id(_: Option<CFType>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         // FIXME(pcwalton): Is this right?
         0
     }

src/boolean.rs

@@ -60,7 +60,7 @@ impl TCFType<CFBooleanRef> for CFBoolean {
     }
 
     #[inline]
-    fn type_id(_: Option<CFBoolean>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFBooleanGetTypeID()
         }

src/bundle.rs

@@ -61,7 +61,7 @@ impl TCFType<CFBundleRef> for CFBundle {
     }
 
     #[inline]
-    fn type_id(_: Option<CFBundle>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFBundleGetTypeID()
         }

src/data.rs

@@ -60,7 +60,7 @@ impl TCFType<CFDataRef> for CFData {
     }
 
     #[inline]
-    fn type_id(_: Option<CFData>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFDataGetTypeID()
         }

src/dictionary.rs

@@ -92,7 +92,7 @@ impl TCFType<CFDictionaryRef> for CFDictionary {
     }
 
     #[inline]
-    fn type_id(_: Option<CFDictionary>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFDictionaryGetTypeID()
         }

src/number.rs

@@ -85,7 +85,7 @@ impl TCFType<CFNumberRef> for CFNumber {
     }
 
     #[inline]
-    fn type_id(_: Option<CFNumber>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFNumberGetTypeID()
         }

src/runloop.rs

@@ -59,7 +59,7 @@ impl TCFType<CFRunLoopRef> for CFRunLoop {
     }
 
     #[inline]
-    fn type_id(_: Option<CFRunLoop>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFRunLoopGetTypeID()
         }
@@ -246,7 +246,7 @@ impl TCFType<CFRunLoopTimerRef> for CFRunLoopTimer {
     }
 
     #[inline]
-    fn type_id(_: Option<CFRunLoopTimer>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFRunLoopTimerGetTypeID()
         }

src/set.rs

@@ -79,7 +79,7 @@ impl TCFType<CFSetRef> for CFSet {
     }
 
     #[inline]
-    fn type_id(_: Option<CFSet>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFSetGetTypeID()
         }

src/string.rs

@@ -255,7 +255,7 @@ impl TCFType<CFStringRef> for CFString {
     }
 
     #[inline]
-    fn type_id(_: Option<CFString>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFStringGetTypeID()
         }

src/url.rs

@@ -62,7 +62,7 @@ impl TCFType<CFURLRef> for CFURL {
     }
 
     #[inline]
-    fn type_id(_: Option<CFURL>) -> CFTypeID {
+    fn type_id() -> CFTypeID {
         unsafe {
             CFURLGetTypeID()
         }