--- title: Replace summary: An in-progress Replace operation. url: https://www.fastly.com/documentation/reference/compute/sdks/cpp/fastly/cache/core/class.Replace/ --- **Kind:** Class **Module:** [core](https://www.fastly.com/documentation/reference/compute/sdks/cpp/fastly/cache/core/) **Package:** compute-sdk-cpp 0.7.0 **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1101 Include `fastly/cache/core.h` to use this class. An in-progress [Replace](https://www.fastly.com/documentation/reference/compute/sdks/cpp/fastly/cache/core/class.Replace/) operation. This type is returned from [`ReplaceBuilder::begin()`](https://www.fastly.com/documentation/reference/compute/sdks/cpp/fastly/cache/core/class.ReplaceBuilder/#method-begin). ## Methods ### deliver_node_max_age **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1212 ```cpp Replace fastly::cache::core::Replace::deliver_node_max_age(std::chrono::nanoseconds duration) && ``` Sets the maximum time the cached item may live on a deliver node in a POP. **Parameters** - `duration`: `std::chrono::nanoseconds` **Returns** `Replace` ### execute **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1110 ```cpp tl::expected fastly::cache::core::Replace::execute(std::chrono::nanoseconds max_age) && ``` Finish using the existing object and start writing a replacement object to the `StreamingBody`. The required `max_age` argument is the "time to live" for the replacement cache item: the time for which the item will be considered fresh, starting from the start of its history (now, unless `initial_age` was provided). **Parameters** - `max_age`: `std::chrono::nanoseconds` **Returns** `tl::expected` ### existing_object **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1113 ```cpp const std::optional & fastly::cache::core::Replace::existing_object() const ``` The existing object, if one exists. The existing object may be stale. **Returns** `const std::optional &` ### header **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1166 ```cpp Replace fastly::cache::core::Replace::header(std::string_view name, const http::HeaderValue &value) && ``` Sets a single-value header for this lookup, discarding any previous values associated with the header `name`. Note: These headers are narrowly useful for implementing cache lookups incorporating the semantics of the [HTTP Vary](https://www.rfc-editor.org/rfc/rfc9110#section-12.5.5) header, but the APIs in this module are not suitable for HTTP caching out-of-the-box. Future SDK releases will contain an HTTP Cache API. The headers act as additional factors in object selection, and the choice of which headers to factor in is determined during insertion, via e.g. `crate::cache::core::InsertBuilder::vary_by`. A lookup will succeed when there is at least one cached item that matches lookup’s cache key, and all of the lookup’s headers included in the cache items’ vary_by list match the corresponding headers in that cached item. A typical example is a cached HTTP response, where the request had an Accept-Encoding header. In that case, the origin server may or may not decide on a given encoding, and whether that same response is suitable for a request with a different (or missing) Accept-Encoding header is determined by whether Accept-Encoding is listed in Vary header in the origin’s response. **Parameters** - `name`: `std::string_view` - `value`: `const http::HeaderValue &` **Returns** `Replace` ### header_values **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1139 ```cpp Replace fastly::cache::core::Replace::header_values(std::string_view name, std::span values) && ``` Sets a multi-value header for this lookup, discarding any previous values associated with the header name. Note: These headers are narrowly useful for implementing cache lookups incorporating the semantics of the [HTTP Vary](https://www.rfc-editor.org/rfc/rfc9110#section-12.5.5) header, but the APIs in this module are not suitable for HTTP caching out-of-the-box. Future SDK releases will contain an HTTP Cache API. The headers act as additional factors in object selection, and the choice of which headers to factor in is determined during insertion, via e.g. `crate::cache::core::InsertBuilder::vary_by`. A lookup will succeed when there is at least one cached item that matches lookup’s cache key, and all of the lookup’s headers included in the cache items’ vary_by list match the corresponding headers in that cached item. A typical example is a cached HTTP response, where the request had an Accept-Encoding header. In that case, the origin server may or may not decide on a given encoding, and whether that same response is suitable for a request with a different (or missing) Accept-Encoding header is determined by whether Accept-Encoding is listed in Vary header in the origin’s response. **Parameters** - `name`: `std::string_view` - `values`: `std::span` **Returns** `Replace` ### initial_age **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1173 ```cpp Replace fastly::cache::core::Replace::initial_age(std::chrono::nanoseconds age) && ``` Sets the initial age of the cached item, to be used in freshness calculations. The initial age is zero by default. **Parameters** - `age`: `std::chrono::nanoseconds` **Returns** `Replace` ### known_length **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1197 ```cpp Replace fastly::cache::core::Replace::known_length(std::uint64_t length) && ``` Sets the known length of the cached item. **Parameters** - `length`: `std::uint64_t` **Returns** `Replace` ### sensitive_data **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1209 ```cpp Replace fastly::cache::core::Replace::sensitive_data(bool is_sensitive) && ``` Enable or disable PCI/HIPAA-compliant non-volatile caching. By default, this is false. See the [Fastly PCI-Compliant Caching and Delivery documentation](https://docs.fastly.com/products/pci-compliant-caching-and-delivery) for details. **Parameters** - `is_sensitive`: `bool` **Returns** `Replace` ### stale_while_revalidate **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1177 ```cpp Replace fastly::cache::core::Replace::stale_while_revalidate(std::chrono::nanoseconds duration) && ``` Sets the time for which a cached item can safely be used despite being considered stale. **Parameters** - `duration`: `std::chrono::nanoseconds` **Returns** `Replace` ### surrogate_keys **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1194 ```cpp Replace fastly::cache::core::Replace::surrogate_keys(std::vector keys) && ``` Sets the surrogate keys that can be used for purging this cached item. Surrogate key purges are the only means to purge specific items from the cache. At least one surrogate key must be set in order to remove an item without performing a [purge-all](https://www.fastly.com/documentation/guides/concepts/cache/purging/#purge-all), waiting for the item’s TTL to elapse, or overwriting the item with `crate::cache::core::insert()`. Surrogate keys must contain only printable ASCII characters (those between 0x21 and 0x7E, inclusive). Any invalid keys will be ignored. See the [Fastly surrogate keys guide](https://www.fastly.com/documentation/guides/full-site-delivery/purging/working-with-surrogate-keys/) for details. **Parameters** - `keys`: `std::vector` **Returns** `Replace` ### user_metadata **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1200 ```cpp Replace fastly::cache::core::Replace::user_metadata(std::vector metadata) && ``` Sets the user-defined metadata to associate with the cached item. **Parameters** - `metadata`: `std::vector` **Returns** `Replace` ### vary_by **Source:** https://github.com/fastly/compute-sdk-cpp/blob/ff911e47be2f319e83a9cde960d2c3c5db534280/include/fastly/cache/core.h#L1169 ```cpp Replace fastly::cache::core::Replace::vary_by(std::vector headers) && ``` Sets the list of headers that must match when looking up this cached item. **Parameters** - `headers`: `std::vector` **Returns** `Replace`