data: add Static and Ignored types

sx/__init__.py

@@ -4,7 +4,7 @@ from .core.io import Stream, Segment
 from .core.meta import Wrapper, Generic
 from .core.expr import Expr
 
-from .types.data import Nothing, Data, data
+from .types.data import Nothing, Static, Ignored, Data, data
 from .types.num import *
 from .types.str import Str, StrType
 from .types.struct import StructType, Struct
@@ -19,7 +19,8 @@ __all__ = [x.__name__ for x in {
     Wrapper, Default, Sized, Ref, Transform, Mapped, Enum,
     Switch, If,
     AlignTo, AlignedTo,
-    Nothing, Data,
+    Nothing, Data, Static, Ignored,
+
     Int, Bool, Float, Str, StrType,
     Arr, Tuple, 
     StructType, Struct, Generic,

sx/types/data.py

@@ -1,6 +1,8 @@
-from typing import Optional as O, Union as U
+from typing import Optional as O, Union as U, Any, Generic as G, TypeVar
 from ..core.base import Type, Context, PossibleDynamic as D
 from ..core.io import Stream, Pos
+from ..core.meta import Wrapper
+from ..core.expr import BaseExpr
 
 
 class Nothing(Type[None]):
@@ -50,3 +52,47 @@ class Data(Type[bytes]):
         return context.peek(self.size)
 
 data = Data()
+
+
+T = TypeVar('T')
+
+class Static(G[T], Type[T]):
+    def __init__(self, value: U[BaseExpr[T], T]) -> None:
+        self.value = value
+
+    def parse(self, context: Context, stream: Stream) -> T:
+        return context.get(self.value)
+
+    def dump(self, context: Context, stream: Stream, value: T) -> None:
+        context.put(self.value, value)
+
+    def sizeof(self, context: Cntext, value: O[T]) -> O[Pos]:
+        return 0
+
+    def default(self, context: Context) -> T:
+        return context.peek(self.value)
+
+    def __str__(self) -> str:
+        return f'={self.value}'
+
+    def __repr__(self) -> str:
+        return f'{__name__}.Static({self.value!r})'
+
+class Ignored(G[T], Wrapper[T]):
+    def __init__(self, child: Type[T]) -> None:
+        super().__init__(child)
+
+    def parse(self, context: Context, stream: Stream) -> None:
+        super().parse(context, stream)
+
+    def emit(self, context: Context, stream: Stream, value: None) -> None:
+        super().emit(context, stream, super().default(context))
+
+    def default(self, context: Context) -> None:
+        return None
+
+    def __str__(self) -> str:
+        return f'(void){super().__str__()}'
+
+    def __repr__(self) -> str:
+        return f'{__name__}.Ignored({super().__repr__()}'