getter.h File Reference

Type-safe field-model reader for VLink topics. More...

#include <functional>
#include <memory>
#include <mutex>
#include <optional>
#include <string>
#include "./base/condition_variable.h"
#include "./impl/getter_impl.h"
#include "./node.h"
#include "./internal/getter-inl.h"

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Classes
class	vlink::Getter< ValueT, SecT >
	Type-safe field reader for the VLink field communication model. More...
class	vlink::SecurityGetter< ValueT >
	Convenience alias for Getter with message security enabled. More...

Namespaces
namespace	vlink

Detailed Description

Type-safe field-model reader for VLink topics.

Getter<ValueT, SecT> is the read side of the VLink field model. It maintains the latest value published by any matching Setter on the same URL. Unlike Subscriber, it retains only the most recent value rather than queuing a history of updates.

Field Model Overview

Setter<T>                 Transport Back-end              Getter<T>
    |                          |                               |
    |-- set(value) ----------> |                               |
    |   serialize(value)       |-- latest-value delivery ----> |
    |                          |  (overwrites previous)        |--> listen callback(value)
    |                          |                               |    value_ updated
    |                          |                               |--> get() returns latest

Key Differences: Getter vs Subscriber

Feature	Getter<T>	Subscriber<T>
Value retention	Latest value cached	No caching
Transport role	kGetter	kSubscriber
Blocking read	wait_for_value()	N/A
Change-reporting filter	set_change_reporting(true)	No built-in filter
Cross-transport use	As subscriber: mark_as_subscriber()	As getter: mark_as_getter()

Usage Patterns

// Pattern 1: polling
Getter<int> g("shm://my_field");
if (auto v = g.get()) {
    std::cout << "value: " << *v << std::endl;
}
 
// Pattern 2: blocking wait
if (g.wait_for_value()) {
    auto v = g.get();
}
 
// Pattern 3: value-change callback (fires when Setter writes a new value)
g.listen([](const int& v) { std::cout << "updated: " << v << std::endl; });
 
// Pattern 4: change-only reporting (suppress duplicate values)
g.set_change_reporting(true);
g.listen([](const int& v) { ... });

Note

get() and wait_for_value() both require a prior Setter write to return a value. Before any Setter has written, get() returns std::nullopt and wait_for_value() blocks until one does.

Template Parameters

ValueT	Value type. Must satisfy Serializer::is_supported().
SecT	Security mode; defaults to SecurityType::kWithoutSecurity.