.. _stdlib_build_const:

============================
Compile-time build constants
============================

.. das:module:: build_const

The BUILD_CONST module provides compile-time constants from the build
environment. Each ``build_*`` accessor is a call macro that reads the daslang
process's command line or environment variables while the requiring module
compiles, and splices the answer into the code as a literal — feed a global
``let`` and gate code with ``static_if`` to erase the disabled branch entirely.
Interpreted and JIT runs resolve the constants per launch; an ``-exe`` build
bakes them at build time.

All functions and symbols are in "build_const" module, use require to get access to it.

.. code-block:: das

    require daslib/build_const



+++++++++++
Call macros
+++++++++++

.. _call-macro-build_const-build_arg_int:

.. das:attribute:: build_arg_int

``build_arg_int(flag, dflt)`` — integer form of ``build_arg_value``; garbage is a compile error.


.. _call-macro-build_const-build_env_flag:

.. das:attribute:: build_env_flag

``build_env_flag(name)`` — boolean env rule: unset/""/0/false/off/no are false, anything else true.


.. _call-macro-build_const-build_flag:

.. das:attribute:: build_flag

``build_flag(flag, env)`` — both-carrier boolean: true when ``flag`` is on the command line, else the env rule on ``env``.


.. _call-macro-build_const-build_arg_value:

.. das:attribute:: build_arg_value

``build_arg_value(flag, dflt)`` — the ``--name value`` / ``--name=value`` argument, or ``dflt``.


.. _call-macro-build_const-build_int:

.. das:attribute:: build_int

``build_int(flag, env, dflt)`` — both-carrier integer; a garbage value on either carrier is a compile error.


.. _call-macro-build_const-build_has_arg:

.. das:attribute:: build_has_arg

``build_has_arg(flag)`` — true when ``flag`` appears verbatim on the command line.


.. _call-macro-build_const-build_env_int:

.. das:attribute:: build_env_int

``build_env_int(name, dflt)`` — integer env value; set-but-empty is ``dflt``, garbage is a compile error.


.. _call-macro-build_const-build_env_value:

.. das:attribute:: build_env_value

``build_env_value(name, dflt)`` — the environment value, or ``dflt`` when unset or empty.


.. _call-macro-build_const-build_value:

.. das:attribute:: build_value

``build_value(flag, env, dflt)`` — both-carrier string: command line beats environment beats ``dflt``.