MAINT: switch to @unevaluated where possible (#382)

* FIX: stabilize hash of `@unevaluated` expression classes
* MAINT: define all array classes with `@unevaluated`
* MAINT: define `EnergyDependentWidth` with `@unevaluated`
* MAINT: define phase space protocols with `unevaluated`

src/ampform/dynamics/__init__.py

@@ -9,7 +9,6 @@
 from typing import TYPE_CHECKING, Any, ClassVar
 
 import sympy as sp
-from sympy.core.basic import _aresame
 
 # pyright: reportUnusedImport=false
 from ampform.dynamics.phasespace import (
@@ -22,12 +21,7 @@
     PhaseSpaceFactorSWave,  # noqa: F401
     _indices_to_subscript,
 )
-from ampform.sympy import (
-    UnevaluatedExpression,
-    determine_indices,
-    implement_doit_method,
-    unevaluated,
-)
+from ampform.sympy import argument, determine_indices, unevaluated
 
 if TYPE_CHECKING:
     from sympy.printing.latex import LatexPrinter
@@ -139,8 +133,8 @@ def evaluate(self) -> sp.Expr:
         ])
 
 
-@implement_doit_method
-class EnergyDependentWidth(UnevaluatedExpression):
+@unevaluated
+class EnergyDependentWidth(sp.Expr):
     r"""Mass-dependent width, coupled to the pole position of the resonance.
 
     See Equation (50.28) in :pdg-review:`2021; Resonances; p.9` and
@@ -154,50 +148,17 @@ class EnergyDependentWidth(UnevaluatedExpression):
     :math:`\left(q/q_0\right)^{2L}` in the definition for :math:`\Gamma(m)`.
     """
 
-    # https://github.com/sympy/sympy/blob/1.8/sympy/core/basic.py#L74-L77
-    __slots__ = ("phsp_factor",)
-    phsp_factor: PhaseSpaceFactorProtocol
-    is_commutative = True
-
-    def __new__(
-        cls,
-        s,
-        mass0,
-        gamma0,
-        m_a,
-        m_b,
-        angular_momentum,
-        meson_radius,
-        phsp_factor: PhaseSpaceFactorProtocol | None = None,
-        name: str | None = None,
-        evaluate: bool = False,
-    ) -> EnergyDependentWidth:
-        args = sp.sympify((s, mass0, gamma0, m_a, m_b, angular_momentum, meson_radius))
-        if phsp_factor is None:
-            phsp_factor = PhaseSpaceFactor
-        # Overwritting Basic.__new__ to store phase space factor type
-        # https://github.com/sympy/sympy/blob/1.10/sympy/core/basic.py#L121-L127
-        expr = object.__new__(cls)
-        expr._assumptions = cls.default_assumptions  # type: ignore[attr-defined]
-        expr._mhash = None
-        expr._args = args
-        expr._name = name
-        expr.phsp_factor = phsp_factor
-        if evaluate:
-            return expr.evaluate()  # type: ignore[return-value]
-        return expr
-
-    def __getnewargs_ex__(self) -> tuple[tuple, dict]:
-        # Pickling support, see
-        # https://github.com/sympy/sympy/blob/1.10/sympy/core/basic.py#L132-L133
-        args = (*self.args, self.phsp_factor)
-        kwargs = {"name": self._name}
-        return args, kwargs
-
-    def _hashable_content(self) -> tuple:
-        # https://github.com/sympy/sympy/blob/1.10/sympy/core/basic.py#L157-L165
-        # phsp_factor is converted to string because of unstable hash for classes
-        return (*super()._hashable_content(), str(self.phsp_factor))
+    s: Any
+    mass0: Any
+    gamma0: Any
+    m_a: Any
+    m_b: Any
+    angular_momentum: Any
+    meson_radius: Any
+    phsp_factor: PhaseSpaceFactorProtocol = argument(
+        default=PhaseSpaceFactor, sympify=False
+    )
+    name: str | None = argument(default=None, sympify=False)
 
     def evaluate(self) -> sp.Expr:
         s, mass0, gamma0, m_a, m_b, angular_momentum, meson_radius = self.args
@@ -215,48 +176,13 @@ def evaluate(self) -> sp.Expr:
         rho0 = self.phsp_factor(mass0**2, m_a, m_b)  # type: ignore[operator]
         return gamma0 * (form_factor_sq / form_factor0_sq) * (rho / rho0)
 
-    def _latex(self, printer: LatexPrinter, *args) -> str:
+    def _latex_repr_(self, printer: LatexPrinter, *args) -> str:
         s = printer._print(self.args[0])
         gamma0 = self.args[2]
         subscript = _indices_to_subscript(determine_indices(gamma0))
-        name = Rf"\Gamma{subscript}" if self._name is None else self._name
+        name = Rf"\Gamma{subscript}" if self.name is None else self.name
         return Rf"{name}\left({s}\right)"
 
-    def _eval_subs(self, old, new):
-        # https://github.com/ComPWA/sympy/blob/bd0cf9a/sympy/core/basic.py#L1074-L1104
-        hit = False
-        new_args = list(self.args)
-        for i, arg in enumerate(self.args):
-            if not hasattr(arg, "_eval_subs"):
-                continue
-            arg = arg._subs(old, new)
-            if not _aresame(arg, new_args[i]):
-                hit = True
-                new_args[i] = arg
-        if hit:
-            return self.func(*new_args, self.phsp_factor, self._name)
-        return self
-
-    def _xreplace(self, rule):
-        # https://github.com/sympy/sympy/blob/bd0cf9a/sympy/core/basic.py#L1190-L1210
-        if self in rule:
-            return rule[self], True
-        if rule:
-            new_args = []
-            hit = False
-            for a in self.args:
-                _xreplace = getattr(a, "_xreplace", None)
-                if _xreplace is not None:
-                    a_xr = _xreplace(rule)
-                    new_args.append(a_xr[0])
-                    hit |= a_xr[1]
-                else:
-                    new_args.append(a)
-            new_args = tuple(new_args)
-            if hit:
-                return self.func(*new_args, self.phsp_factor, self._name), True
-        return self, False
-
 
 def relativistic_breit_wigner(s, mass0, gamma0) -> sp.Expr:
     """Relativistic Breit-Wigner lineshape.
@@ -275,7 +201,7 @@ def relativistic_breit_wigner_with_ff(
     m_b,
     angular_momentum,
     meson_radius,
-    phsp_factor: PhaseSpaceFactorProtocol | None = None,
+    phsp_factor: PhaseSpaceFactorProtocol = PhaseSpaceFactor,
 ) -> sp.Expr:
     """Relativistic Breit-Wigner with `.BlattWeisskopfSquared` factor.
 

src/ampform/dynamics/kmatrix.py

@@ -116,7 +116,7 @@ def parametrization(
         pole_id,
         angular_momentum=0,
         meson_radius=1,
-        phsp_factor: PhaseSpaceFactorProtocol | None = None,
+        phsp_factor: PhaseSpaceFactorProtocol = PhaseSpaceFactor,
     ) -> sp.Expr:
         def residue_function(pole_id, i) -> sp.Expr:
             return residue_constant[pole_id, i] * sp.sqrt(