[petlenz]

What

core/parameter_helpers.h:

required<value_type>(para, "K");
optional<value_type>(para, "q", value_type{2.5});

These replace para.template insert<T>(key).template add<is_required>() / add<set_default>(v). They are additive (existing materials compile unchanged) and return the parameter, so checks or a description can be chained. They are also the place to attach check_data_type/range<> later (#65).

linear_isotropic_hardening and exponential_isotropic_hardening use them, as a demonstration. The other materials are not converted here: most of their files are touched by the open PRs #79–#86, so they can follow one at a time after those merge.

The reading side (base::template get_parameter<T>) is not changed; a helper for it needs material_base.h, which #86 changes.

Tests

ParameterHelpers.RequiredAndOptionalDeclareTheParameters (in test_set_parameter.cpp): a missing required parameter throws, defaults are applied, and a given value is kept. It failed to compile before. GCC 14 Debug with fetched dependencies: 622/622.

Closes #74

[petlenz]

Review findings (design, tmech expressions instead of component loops, modern C++, comments, tests, correctness). Severity: must = wrong result, hang, build break or unreachable feature; should = design, duplication, accuracy; nit = style.

required/optional helpers — ready

• [should] optional collides with std::optional by name → with_default/optional_parameter; helpers are numsim-core material, consider upstreaming; 119 .template insert< sites remain — track the follow-up.