libdpf/doc/pages/programmability.md

# Programmability {#programmability}

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<div class="eli5"><b>ELI5.</b> A wildcard is a placeholder with the correction word not yet fixed. Assigning an input or a leaf is a Beaver multiplication against that placeholder: one blinded share is exchanged, then both parties write the same correction. An updatable leaf can be patched again the same way.</div>
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Fill in a secret index or payload after the key exists, rewrite an
updatable leaf, or commit to a vector before choosing which coordinate
to open.

| Mechanism | What it does |
| --- | --- |
| [dpf::wildcard_value](@ref dpf/wildcard.hpp) | Placeholder input or leaf. Eval throws until you assign. |
| Leaf assign | `compute_and_get_blinded_output_share`, `reconstruct_correction_word`, `async_assign_leaf`, `assign_cmp` — see [wildcard assign](@ref wildcard_assign). |
| [dpf::updatable](@ref dpf/placement.hpp) | Beaver leaf so a later rewrite replaces the payload without regenerating the spine. |
| [dpf::ppvc](@ref ppvc_manual) | Point-programmable vector commitment: bind `(Z/2^s Z)^n`, then open one hidden coordinate (or the sum). |
| [dpf::at](@ref dpf/placement.hpp) / `idpf` | Plant values on public prefixes as well as the leaf. |

```cpp
auto [k0, k1] = dpf::make_dpf(
    std::uint8_t{12},
    dpf::wildcard_value<std::uint32_t>{});
// assign the payload later; eval before assign throws

using scheme = dpf::ppvc<std::uint8_t, 8>;
const auto pp = scheme::setup();
const auto [com, st] = scheme::commit(pp);
const auto op = scheme::open(st, 0, 0x5a, std::uint8_t{40});
```

**Go deeper:** [guided tour — wildcards](@ref tour_outputs),
[PPVC](@ref tour_ppvc), [PPVC manual](@ref ppvc_manual),
[input types](@ref input_types), [output types](@ref output_types).