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From Christofer Dutz <>
Subject Re: Define execute operation on Request; remove read/write operations from Reader/Writer
Date Wed, 12 Sep 2018 14:21:26 GMT
Hi Andrey,

are you proposing a Factory-Factory? Wouldn't that go a little too far? Currently the request
factory method being in the connection, is just an implementation detail we could have a S7Reader
class implementing the Reader interface and this is generated from the connection, if this
is the problem.


Am 12.09.18, 15:54 schrieb "Andrey Skorikov" <>:

    Hi Sebastian,
    good point! The mutability of PlcReadRequest would be a consequence of 
    the mutability of the PlcConnection (or something that can handle the 
    execute). However, in order to construct a immutable PlcReadRequest, 
    currently we still need to obtain a PlcRequest.Builder from the same 
    mutable PlcConnection. I think, if we really want PlcReadRequest to be 
    immutable, then we should be able to construct them independently (not 
    from a mutalbe object). Perhaps we could separate PlcRequest 
    construction from its exection by providing a RequestBuilder factory 
    method not on a mutable PlcConnection but "higher up", for example 
    somewhere on a PlcDriver?
    On 09/12/2018 03:33 PM, Sebastian Rühl wrote:
    > Hey Andrey,
    > One thing that would stand against this: Adding a execute() would make the PlcReadRequest
mutable which is a thing we should avoid (Mutable because it would need a reference store
to something that can handle the execute).
    > FYI: I added a mutability test into plc4j-api (which should be added to plc4j-driver-bases
after the refactoring) which tests all Items for mutability. Currently we have some open issues
regarding that.
    > Sebastian
    >> Am 12.09.2018 um 14:50 schrieb Andrey Skorikov <>:
    >> Hello,
    >> currently, PlcReadRequests and PlcWriteRequests are executed by invoking the
corresponding read/write operation on the PlcReader/PlcWriter objects. Hence the typical workflow
for reading a value contains the following steps:
    >> 1. Obtain a PlcReader instance from a PlcConnection
    >> 2. Obtain a Builder by invoking readRequestBuilder() on PlcReader
    >> 3. Build a request using the Builder
    >> 4. Execute the request by invoking read() on the PlcReader, passing the constructed
request as argument
    >> PlcReader reader = ... // obtain reader
    >> PlcReadRequest request = reader.readRequestBuilder().addItem(...).build();
    >> Future<PlcReadResponse> response =;
    >> Since we only can build a request throgh a PlcReader instance, invoking the read
operation on the PlcReader is redundant. Therefore I suggest removing the read/write operation
from the PlcReader/PlcWriter and defining a execute() operation on PlcRequest instead. The
workflow would look like this then:
    >> PlcReader reader = ... // obtain reader
    >> PlcReadRequest request = reader.readRequestBuilder().addItem(...).build();
    >> Future<PlcReadResponse> response = request.execute();
    >> Please note that there is no more need to "keep" a reference to PlcReader in
this context, since it is implicitly associated with the request by calling reader.readRequestBuilder().build().
    >> Best regards,
    >> Andrey

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