# Solver graph edges

Edges carry data between nodes in a solver graph. They live in
`shamrock::solvergraph` and inherit
[`IEdge`](../../../src/shamsolvergraph/include/shamsolvergraph/edge/IEdge.hpp)
(or [`IEdgeNamed`](../../../src/shamsolvergraph/include/shamsolvergraph/edge/IEdgeNamed.hpp)).

Every edge must implement `free_alloc()` and the label/TeX hooks.

## Derive from `IEdge`

Implement the three required overrides:

```cpp
class MyEdge : public shamrock::solvergraph::IEdge {
  public:
    // 1. DOT label
    std::string _impl_get_dot_label() const override { return "MyEdge"; }
    // 2. TeX symbol
    std::string _impl_get_tex_symbol() const override { return "e"; }
    // 3. free allocated resources
    void free_alloc() override { /* ... */ }
};
```

`get_label()` and `get_tex_symbol()` call the `_impl_*` methods.

## Derive from `IEdgeNamed`

`IEdgeNamed` stores a label and a TeX symbol, and already implements
`_impl_get_dot_label` / `_impl_get_tex_symbol`. Subclasses inherit the
constructor and only add payload + `free_alloc()`.

```cpp
class MyNamedEdge : public shamrock::solvergraph::IEdgeNamed {
  public:
    using IEdgeNamed::IEdgeNamed; // takes (label, tex_symbol)

    void free_alloc() override { /* ... */ }
};

// usage — first arg is the DOT label, second is the TeX symbol
std::string label      = "my_edge";
std::string tex_symbol = "e";
auto e = std::make_shared<MyNamedEdge>(label, tex_symbol);
```

[`IDataEdge<T>`](../../../src/shamsolvergraph/include/shamsolvergraph/edge/IDataEdge.hpp)
is the common named edge with a `T data` payload:

```cpp
auto e = shamrock::solvergraph::IDataEdge<f64>::make_shared(label, tex_symbol);
e->data = 1.0;
```

## Related files

- [`IEdge.hpp`](../../../src/shamsolvergraph/include/shamsolvergraph/edge/IEdge.hpp)
- [`IEdgeNamed.hpp`](../../../src/shamsolvergraph/include/shamsolvergraph/edge/IEdgeNamed.hpp)
- [`IDataEdge.hpp`](../../../src/shamsolvergraph/include/shamsolvergraph/edge/IDataEdge.hpp)
- [`IEdge_tests.cpp`](../../../src/tests/shamsolvergraph/edge/IEdge_tests.cpp)