some cleanup

 - move numpy_struct to class composer and use its sequencers
 - fix some type errors

src/pystencilssfg/composer/basic_composer.py

 from __future__ import annotations
 from typing import Sequence, TypeAlias
 from abc import ABC, abstractmethod
-import numpy as np
 import sympy as sp
 from functools import reduce
 from warnings import warn
@@ -33,10 +32,6 @@ from ..ir.source_components import (
     SfgFunction,
     SfgKernelNamespace,
     SfgKernelHandle,
-    SfgClass,
-    SfgConstructor,
-    SfgMemberVariable,
-    SfgClassKeyword,
     SfgEntityDecl,
     SfgEntityDef,
     SfgNamespaceBlock,
@@ -86,7 +81,7 @@ SequencerArg: TypeAlias = tuple | ExprLike | SfgCallTreeNode | SfgNodeBuilder
 class KernelsAdder:
     def __init__(self, ctx: SfgContext, loc: SfgNamespaceBlock):
         self._ctx = ctx
-        self._loc = SfgNamespaceBlock
+        self._loc = loc
         assert isinstance(loc.namespace, SfgKernelNamespace)
         self._kernel_namespace = loc.namespace
 
@@ -110,6 +105,8 @@ class KernelsAdder:
         khandle = SfgKernelHandle(kernel_name, self._kernel_namespace, kernel)
         self._kernel_namespace.add_kernel(khandle)
 
+        self._loc.elements.append(SfgEntityDef(khandle))
+
         for header in kernel.required_headers:
             assert self._ctx.impl_file is not None
             self._ctx.impl_file.includes.append(HeaderFile.parse(header))
@@ -242,7 +239,7 @@ class SfgBasicComposer(SfgIComposer):
         self._cursor.write_impl(kns_block)
         return KernelsAdder(self._ctx, kns_block)
 
-    def include(self, header_file: str | HeaderFile, private: bool = False):
+    def include(self, header: str | HeaderFile, private: bool = False):
         """Include a header file.
 
         Args:
@@ -262,7 +259,7 @@ class SfgBasicComposer(SfgIComposer):
                 #include <vector>
                 #include "custom.h"
         """
-        header_file = HeaderFile.parse(header_file)
+        header_file = HeaderFile.parse(header)
 
         if private:
             if self._ctx.impl_file is None:
@@ -273,21 +270,6 @@ class SfgBasicComposer(SfgIComposer):
         else:
             self._ctx.header_file.includes.append(header_file)
 
-    def numpy_struct(
-        self, name: str, dtype: np.dtype, add_constructor: bool = True
-    ) -> SfgClass:
-        """Add a numpy structured data type as a C++ struct
-
-        Returns:
-            The created class object
-        """
-        cls = self._struct_from_numpy_dtype(
-            name, dtype, add_constructor=add_constructor
-        )
-        self._cursor.add_entity(cls)
-        self._cursor.write_header(SfgEntityDecl(cls))
-        return cls
-
     def kernel_function(self, name: str, kernel: Kernel | SfgKernelHandle):
         """Create a function comprising just a single kernel call.
 
@@ -295,9 +277,11 @@ class SfgBasicComposer(SfgIComposer):
             ast_or_kernel_handle: Either a pystencils AST, or a kernel handle for an already registered AST.
         """
         if isinstance(kernel, Kernel):
-            kernel = self.kernels.add(kernel, name)
+            khandle = self.kernels.add(kernel, name)
+        else:
+            khandle = kernel
 
-        self.function(name)(self.call(kernel))
+        self.function(name)(self.call(khandle))
 
     def function(
         self,
@@ -536,41 +520,6 @@ class SfgBasicComposer(SfgIComposer):
         ]
         return SfgDeferredVectorMapping(components, rhs)
 
-    def _struct_from_numpy_dtype(
-        self, struct_name: str, dtype: np.dtype, add_constructor: bool = True
-    ):
-        cls = SfgClass(
-            struct_name,
-            self._cursor.current_namespace,
-            class_keyword=SfgClassKeyword.STRUCT,
-        )
-
-        fields = dtype.fields
-        if fields is None:
-            raise SfgException(f"Numpy dtype {dtype} is not a structured type.")
-
-        constr_params = []
-        constr_inits = []
-
-        for member_name, type_info in fields.items():
-            member_type = create_type(type_info[0])
-
-            member = SfgMemberVariable(member_name, member_type)
-
-            arg = SfgVar(f"{member_name}_", member_type)
-
-            cls.default.append_member(member)
-
-            constr_params.append(arg)
-            constr_inits.append(f"{member}({arg})")
-
-        if add_constructor:
-            cls.default.append_member(
-                SfgEntityDef(SfgConstructor(constr_params, constr_inits))
-            )
-
-        return cls
-
 
 def make_statements(arg: ExprLike) -> SfgStatements:
     return SfgStatements(str(arg), (), depends(arg), includes(arg))

src/pystencilssfg/composer/class_composer.py

 from __future__ import annotations
 from typing import Sequence
 from itertools import takewhile, dropwhile
+import numpy as np
 
 from pystencils.types import PsCustomType, UserTypeSpec, create_type
 
@@ -196,6 +197,16 @@ class SfgClassComposer(SfgComposerMixIn):
         """
         return self._class(class_name, SfgClassKeyword.STRUCT, bases)
 
+    def numpy_struct(
+        self, name: str, dtype: np.dtype, add_constructor: bool = True
+    ):
+        """Add a numpy structured data type as a C++ struct
+
+        Returns:
+            The created class object
+        """
+        return self._struct_from_numpy_dtype(name, dtype, add_constructor)
+
     @property
     def public(self) -> SfgClassComposer.VisibilityBlockSequencer:
         """Create a `public` visibility block in a class body"""
@@ -241,6 +252,8 @@ class SfgClassComposer(SfgComposerMixIn):
     #   INTERNALS
 
     def _class(self, class_name: str, keyword: SfgClassKeyword, bases: Sequence[str]):
+        #   TODO: Return a `CppClass` instance representing the generated class
+
         if self._cursor.get_entity(class_name) is not None:
             raise ValueError(
                 f"Another entity with name {class_name} already exists in the current namespace."
@@ -288,3 +301,30 @@ class SfgClassComposer(SfgComposerMixIn):
             self._cursor.write_header(SfgEntityDef(cls))
 
         return sequencer
+
+    def _struct_from_numpy_dtype(
+        self, struct_name: str, dtype: np.dtype, add_constructor: bool = True
+    ):
+        fields = dtype.fields
+        if fields is None:
+            raise SfgException(f"Numpy dtype {dtype} is not a structured type.")
+
+        members: list[SfgClassComposer.ConstructorBuilder | SfgVar] = []
+        if add_constructor:
+            ctor = self.constructor()
+            members.append(ctor)
+
+        for member_name, type_info in fields.items():
+            member_type = create_type(type_info[0])
+
+            member = SfgVar(member_name, member_type)
+            members.append(member)
+
+            if add_constructor:
+                arg = SfgVar(f"{member_name}_", member_type)
+                ctor.add_param(arg)
+                ctor.init(member)(arg)
+
+        return self.struct(
+            struct_name,
+        )(*members)

src/pystencilssfg/ir/__init__.py

@@ -15,8 +15,6 @@ from .call_tree import (
 )
 
 from .source_components import (
-    SfgHeaderInclude,
-    SfgEmptyLines,
     SfgKernelNamespace,
     SfgKernelHandle,
     SfgKernelParamVar,
@@ -25,7 +23,6 @@ from .source_components import (
     SfgClassKeyword,
     SfgClassMember,
     SfgVisibilityBlock,
-    SfgInClassDefinition,
     SfgMemberVariable,
     SfgMethod,
     SfgConstructor,
@@ -47,8 +44,6 @@ __all__ = [
     "SfgBranch",
     "SfgSwitchCase",
     "SfgSwitch",
-    "SfgHeaderInclude",
-    "SfgEmptyLines",
     "SfgKernelNamespace",
     "SfgKernelHandle",
     "SfgKernelParamVar",
@@ -57,7 +52,6 @@ __all__ = [
     "SfgClassKeyword",
     "SfgClassMember",
     "SfgVisibilityBlock",
-    "SfgInClassDefinition",
     "SfgMemberVariable",
     "SfgMethod",
     "SfgConstructor",

src/pystencilssfg/ir/source_components.py

@@ -404,18 +404,7 @@ class SfgConstructor(SfgClassMember):
 
 
 class SfgClass(SfgCodeEntity):
-    """Models a C++ class.
-
-    ### Adding members to classes
-
-    Members are never added directly to a class. Instead, they are added to
-    an [SfgVisibilityBlock][pystencilssfg.source_components.SfgVisibilityBlock]
-    which defines their syntactic position and visibility modifier in the code.
-    At the top of every class, there is a default visibility block
-    accessible through the `default` property.
-    To add members with custom visibility, create a new SfgVisibilityBlock,
-    add members to the block, and add the block using `append_visibility_block`.
-    """
+    """A C++ class."""
 
     __match_args__ = ("class_name",)
 
@@ -524,12 +513,6 @@ class SfgClass(SfgCodeEntity):
         self._member_vars[variable.name] = variable
 
 
-SourceEntity_T = TypeVar(
-    "SourceEntity_T", bound=SfgFunction | SfgClassMember | SfgClass, covariant=True
-)
-"""Source entities that may have declarations and definitions."""
-
-
 #   =========================================================================================================
 #
 #   SYNTACTICAL ELEMENTS
@@ -540,6 +523,12 @@ SourceEntity_T = TypeVar(
 #   =========================================================================================================
 
 
+SourceEntity_T = TypeVar(
+    "SourceEntity_T", bound=SfgKernelHandle | SfgFunction | SfgClassMember | SfgClass, covariant=True
+)
+"""Source entities that may have declarations and definitions."""
+
+
 class SfgEntityDecl(Generic[SourceEntity_T]):
     """Declaration of a function, class, method, or constructor"""