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45 lines
3.1 KiB
Markdown
45 lines
3.1 KiB
Markdown
00---
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title: "Generators"
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---
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Some templates within the ETL are designed to support a variable number of template parameters. To accommodate this, these template classes have a number of specialisations to handle each variant. The ETL sets this number to a reasonable default, but there will almost certainly be circumstances where these are too small for the project at hand.
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To this end, the ETL supplies 'generators' to enable the creation of customised variants of these template classes.
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The code generation is handled by a Python library called `COG`. This allows Python code to be embedded within the C++. When `COG` is run on the generator header, it will produce a customised version of that header.
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The naming convention used is
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The generator file: `xxxx_generator.h`
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The output file: `xxxx.h`
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The script: `generate_xxxx.bat`
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The script `generate.bat` will run all of the generate scripts.
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e.g.
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Running the `COG` script on the generator `type_traits_generator.h` will create `type_traits.h`
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The syntax for processing a generator file is
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`python -m cogapp -d -e -o<output> -D<parameter>=<N> <generator>`
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e.g.
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`python -m cogapp -d -e -otype_traits.h -DIsOneOf=16 type_traits_generator.h`
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The line above will create type_traits.h with the ability to handle up to 16 types in the `etl::is_one_of` structure.
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All of the generator files may be processed by running the script `generate.bat`
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There are generator scripts for each generator header.
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This can be run as a command line batch file under Windows or as a script under Linux (if set to 'executable')
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**Defined generators**
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| Functionality | Generator | Output | Parameters | Notes |
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| -------------------- | ---------------------------- | ------------------ | ---------- | ----- |
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| Finite State Machine | `fsm_generator.h` | `fsm.h` | Handlers | Defines the maximum number of events that can be handled |
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| Message Router | `message_router_generator.h` | `message_router.h` | Handlers | Defines the maximum number of messages that can be handled |
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| Smallest | `smallest_generator.h` | `smallest.h` | NTypes | Defines the maximum number of types that can be declared |
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| Largest | `largest_generator.h` | `largest.h` | NTypes | Defines the maximum number of types that can be declared |
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| Type Traits | `type_traits_generator.h` | `type_traits.h` | NTypes | Defines the maximum number of types that can be declared in the class `etl::is_one_of` |
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| Type Lookup | `type_lookup_generator.h` | `type_lookup.h` | NTypes | Defines the maximum number of types that can be declared in the classes `etl::type_id_lookup` and `etl::type_type_lookup` |
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| Type Select | `type_select_generator.h` | `type_select.h` | NTypes | Defines the maximum number of types that can be declared in the class `etl::type_select` |
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| Variant Pool | `variant_pool_generator.h` | `variant_pool.h` | NTypes | Defines the maximum number of types that can be declared |
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