Thank you for example. I asked about it programmers at work too - PHP guys - and they explained me how you are see usage of that interfaces in my code. They prepare for me some "skeleton" on which i will try to build my solution. Will be back  if i will have some code.

I created interface IfRequestHandler it is used only by one class RequestHandlerXML right now but thanks to such solution i can create more classes with same interface which can handle it in different way.. eg second can be RequestHandlerCSVReport or RequestHandlerSendViaEmail. Is it this what you ware mentioning? Bellow working code:

/////////
//main.d:
/////////

#!/usr/bin/rdmd

import std.stdio, sigv4, conf;



void main()
{
    ResultHandlerXML hand = new ResultHandlerXML;
    SigV4 req = new SigV4(hand);

    //req.ResultHandler = hand;
    req.go();
    hand.processResult();

}

/////////
//conf.d:
/////////

module conf;

import std.stdio, std.process;
import std.net.curl:exit;

interface IfConfig
{
    void set(string val, string var);
    string get(string var);
}


class Config : IfConfig
{
    this()
    {
        this.accKey = environment.get("AWS_ACCESS_KEY");
        if(accKey is null)
        {
            writeln("accessKey not available");
            exit(-1);
        }
        this.secKey = environment.get("AWS_SECRET_KEY");
        if(secKey is null)
        {
            writeln("secretKey not available");
            exit(-1);
        }
    }

    public:

        void set(string val, string var)
        {
            switch(var)
            {
                case "accKey": accKey = val; break;
                case "secKey": secKey = val; break;
                default: writeln("Can not be set, not such value");
            }
        }


        string get(string var)
        {
            string str = "";

            switch(var)
            {
            case "accKey": return accKey;
            case "secKey": return secKey;
            default: writeln("Can not be get, not such value");
            }

            return str;
        }


 //   private:

        string accKey;
        string secKey;

}

/////////
//sigv4.d
/////////

module sigv4;

import std.stdio, std.process;
import std.digest.sha, std.digest.hmac;
import std.string;
import std.conv;
import std.datetime;
import std.net.curl;
import conf;


interface IfSigV4
{
	IfResultHandler go(ResultHandlerXML ResultHandler);
}

interface IfResultHandler
{
        void setResult(int content);
        void processResult();
}

class ResultHandlerXML : IfResultHandler
{
    void setResult(int content)
    {
        this.xmlresult = content;
    }

    void processResult()
    {
        writeln(xmlresult);
    }

    private:
        int xmlresult;
}

class SigV4 : IfSigV4
{
	//could be changed to take some structure as parameter instead of such ammount of attributes

	this(string methodStr = "GET", string serviceStr = "ec2", string hostStr = "ec2.amazonaws.com", string regionStr = "us-east-1", string endpointStr = "https://ec2.amazonaws.com", string payloadStr = "", string parmStr = "Action=DescribeInstances")
	in
	{
		writeln(parmStr);
	}
	body
	{
        conf.Config config = new conf.Config;

		this.method = methodStr;
		this.service = serviceStr;
		this.host = hostStr;
		this.region = regionStr;
		this.endpoint = endpointStr;
		this.payload = payloadStr;
		this.requestParameters = parmStr;

		this.accessKey = config.get("accKey");
		if(accessKey is null)
		{
			writeln("accessKey not available");
			exit(-1);
		}
		this.secretKey = config.get("secKey");
		if(secretKey is null)
                {
                        writeln("secretKey not available");
			exit(-1);
                }

	}

	public:
		string method;
		string service;
		string host;
		string region;
		string endpoint;
		string payload;
		string requestParameters;

		IfResultHandler ResultHandler;




		IfResultHandler go(ResultHandlerXML ResultHandler)
		{
			//time need to be set when we are sending request not before
			auto currentClock = Clock.currTime(UTC());
			auto currentDate = cast(Date)currentClock;
			auto curDateStr = currentDate.toISOString;
			auto currentTime = cast(TimeOfDay)currentClock;
			auto curTimeStr = currentTime.toISOString;
			auto xamztime = curDateStr ~ "T" ~ curTimeStr ~ "Z";

			canonicalURI = "/";
			canonicalQueryString = requestParameters ~ this.Version;
			canonicalHeadersString =  "host:" ~ this.host ~ "\n" ~ "x-amz-date:" ~ xamztime ~ "\n";
			signedHeaders = "host;x-amz-date";

			auto canonicalRequest = getCanonicalRequest(canonicalURI, canonicalQueryString, canonicalHeadersString, signedHeaders);

			string credentialScope = curDateStr ~ "/" ~ region ~ "/" ~ service ~ "/" ~ "aws4_request";

			string stringToSign = algorithm ~ "\n" ~ xamztime ~ "\n" ~ credentialScope ~ "\n" ~ sha256Of(canonicalRequest).toHexString.toLower;

			auto signingKey = getSignatureKey(secretKey, curDateStr, region, service);

			string signature = hmac!SHA256(stringToSign.representation, signingKey).toHexString.toLower;

			string authorizationHeader = algorithm ~ " " ~ "Credential=" ~ accessKey ~ "/" ~ credentialScope ~ ", " ~ "SignedHeaders=" ~ signedHeaders ~ ", " ~ "Signature=" ~ signature;

			auto client = HTTP(endpoint ~ "?" ~ canonicalQueryString);
			client.method = HTTP.Method.get;
			client.addRequestHeader("x-amz-date", xamztime);
			client.addRequestHeader("Authorization", authorizationHeader);
			auto content = client.perform();

            writeln(content);

			ResultHandler.setResult(content);
                        return ResultHandler;
		}

	private:
		const string algorithm = "AWS4-HMAC-SHA256";
		const string Version = "&Version=2013-10-15";

		string accessKey;
		string secretKey;



		string canonicalURI;
		string canonicalQueryString;
	       	string canonicalHeadersString;
	       	string signedHeaders;



		alias sign = hmac!SHA256;

		auto getSignatureKey(string key, string dateStamp, string regionName, string serviceName)
		{
			auto kString = ("AWS4" ~ key).representation;
			auto kDate = sign(dateStamp.representation, kString);
			auto kRegion = sign(regionName.representation, kDate);
			auto kService = sign(serviceName.representation, kRegion);
			auto kSigning = sign("aws4_request".representation, kService);

			return kSigning;
		}


		auto getCanonicalRequest(string canonicalURI, string canonicalQueryString, string canonicalHeadersString, string signedHeaders)
		{
			string payloadHash = sha256Of(payload).toHexString.toLower;
			string canonicalRequest = method ~ "\n" ~ canonicalURI ~ "\n" ~ canonicalQueryString ~ "\n" ~ canonicalHeadersString ~ "\n" ~ signedHeaders ~ "\n" ~ payloadHash;
			return canonicalRequest;
		}
}

On 16/10/15 4:14 PM, holo wrote:
> I created interface IfRequestHandler it is used only by one class
> RequestHandlerXML right now but thanks to such solution i can create
> more classes with same interface which can handle it in different way..
> eg second can be RequestHandlerCSVReport or RequestHandlerSendViaEmail.
> Is it this what you ware mentioning? Bellow working code:
>
> /////////
> //main.d:
> /////////
>
> #!/usr/bin/rdmd
>
> import std.stdio, sigv4, conf;
>
>
>
> void main()
> {
>      ResultHandlerXML hand = new ResultHandlerXML;
>      SigV4 req = new SigV4(hand);
>
>      //req.ResultHandler = hand;
>      req.go();
>      hand.processResult();
>
> }
>
> /////////
> //conf.d:
> /////////
>
> module conf;
>
> import std.stdio, std.process;
> import std.net.curl:exit;
>
> interface IfConfig
> {
>      void set(string val, string var);
>      string get(string var);
> }
>
>
> class Config : IfConfig
> {
>      this()
>      {
>          this.accKey = environment.get("AWS_ACCESS_KEY");
>          if(accKey is null)
>          {
>              writeln("accessKey not available");
>              exit(-1);
>          }
>          this.secKey = environment.get("AWS_SECRET_KEY");
>          if(secKey is null)
>          {
>              writeln("secretKey not available");
>              exit(-1);
>          }
>      }
>
>      public:
>
>          void set(string val, string var)
>          {
>              switch(var)
>              {
>                  case "accKey": accKey = val; break;
>                  case "secKey": secKey = val; break;
>                  default: writeln("Can not be set, not such value");
>              }
>          }
>
>
>          string get(string var)
>          {
>              string str = "";
>
>              switch(var)
>              {
>              case "accKey": return accKey;
>              case "secKey": return secKey;
>              default: writeln("Can not be get, not such value");
>              }
>
>              return str;
>          }
>
>
>   //   private:
>
>          string accKey;
>          string secKey;
>
> }
>
> /////////
> //sigv4.d
> /////////
>
> module sigv4;
>
> import std.stdio, std.process;
> import std.digest.sha, std.digest.hmac;
> import std.string;
> import std.conv;
> import std.datetime;
> import std.net.curl;
> import conf;
>
>
> interface IfSigV4
> {
>      IfResultHandler go(ResultHandlerXML ResultHandler);
> }
>
> interface IfResultHandler
> {
>          void setResult(int content);
>          void processResult();
> }
>
> class ResultHandlerXML : IfResultHandler
> {
>      void setResult(int content)
>      {
>          this.xmlresult = content;
>      }
>
>      void processResult()
>      {
>          writeln(xmlresult);
>      }
>
>      private:
>          int xmlresult;
> }
>
> class SigV4 : IfSigV4
> {
>      //could be changed to take some structure as parameter instead of
> such ammount of attributes
>
>      this(string methodStr = "GET", string serviceStr = "ec2", string
> hostStr = "ec2.amazonaws.com", string regionStr = "us-east-1", string
> endpointStr = "https://ec2.amazonaws.com", string payloadStr = "",
> string parmStr = "Action=DescribeInstances")
>      in
>      {
>          writeln(parmStr);
>      }
>      body
>      {
>          conf.Config config = new conf.Config;
>
>          this.method = methodStr;
>          this.service = serviceStr;
>          this.host = hostStr;
>          this.region = regionStr;
>          this.endpoint = endpointStr;
>          this.payload = payloadStr;
>          this.requestParameters = parmStr;
>
>          this.accessKey = config.get("accKey");
>          if(accessKey is null)
>          {
>              writeln("accessKey not available");
>              exit(-1);
>          }
>          this.secretKey = config.get("secKey");
>          if(secretKey is null)
>                  {
>                          writeln("secretKey not available");
>              exit(-1);
>                  }
>
>      }
>
>      public:
>          string method;
>          string service;
>          string host;
>          string region;
>          string endpoint;
>          string payload;
>          string requestParameters;
>
>          IfResultHandler ResultHandler;
>
>
>
>
>          IfResultHandler go(ResultHandlerXML ResultHandler)
>          {
>              //time need to be set when we are sending request not before
>              auto currentClock = Clock.currTime(UTC());
>              auto currentDate = cast(Date)currentClock;
>              auto curDateStr = currentDate.toISOString;
>              auto currentTime = cast(TimeOfDay)currentClock;
>              auto curTimeStr = currentTime.toISOString;
>              auto xamztime = curDateStr ~ "T" ~ curTimeStr ~ "Z";
>
>              canonicalURI = "/";
>              canonicalQueryString = requestParameters ~ this.Version;
>              canonicalHeadersString =  "host:" ~ this.host ~ "\n" ~
> "x-amz-date:" ~ xamztime ~ "\n";
>              signedHeaders = "host;x-amz-date";
>
>              auto canonicalRequest = getCanonicalRequest(canonicalURI,
> canonicalQueryString, canonicalHeadersString, signedHeaders);
>
>              string credentialScope = curDateStr ~ "/" ~ region ~ "/" ~
> service ~ "/" ~ "aws4_request";
>
>              string stringToSign = algorithm ~ "\n" ~ xamztime ~ "\n" ~
> credentialScope ~ "\n" ~ sha256Of(canonicalRequest).toHexString.toLower;
>
>              auto signingKey = getSignatureKey(secretKey, curDateStr,
> region, service);
>
>              string signature = hmac!SHA256(stringToSign.representation,
> signingKey).toHexString.toLower;
>
>              string authorizationHeader = algorithm ~ " " ~
> "Credential=" ~ accessKey ~ "/" ~ credentialScope ~ ", " ~
> "SignedHeaders=" ~ signedHeaders ~ ", " ~ "Signature=" ~ signature;
>
>              auto client = HTTP(endpoint ~ "?" ~ canonicalQueryString);
>              client.method = HTTP.Method.get;
>              client.addRequestHeader("x-amz-date", xamztime);
>              client.addRequestHeader("Authorization", authorizationHeader);
>              auto content = client.perform();
>
>              writeln(content);
>
>              ResultHandler.setResult(content);
>                          return ResultHandler;
>          }
>
>      private:
>          const string algorithm = "AWS4-HMAC-SHA256";
>          const string Version = "&Version=2013-10-15";
>
>          string accessKey;
>          string secretKey;
>
>
>
>          string canonicalURI;
>          string canonicalQueryString;
>                 string canonicalHeadersString;
>                 string signedHeaders;
>
>
>
>          alias sign = hmac!SHA256;
>
>          auto getSignatureKey(string key, string dateStamp, string
> regionName, string serviceName)
>          {
>              auto kString = ("AWS4" ~ key).representation;
>              auto kDate = sign(dateStamp.representation, kString);
>              auto kRegion = sign(regionName.representation, kDate);
>              auto kService = sign(serviceName.representation, kRegion);
>              auto kSigning = sign("aws4_request".representation, kService);
>
>              return kSigning;
>          }
>
>
>          auto getCanonicalRequest(string canonicalURI, string
> canonicalQueryString, string canonicalHeadersString, string signedHeaders)
>          {
>              string payloadHash = sha256Of(payload).toHexString.toLower;
>              string canonicalRequest = method ~ "\n" ~ canonicalURI ~
> "\n" ~ canonicalQueryString ~ "\n" ~ canonicalHeadersString ~ "\n" ~
> signedHeaders ~ "\n" ~ payloadHash;
>              return canonicalRequest;
>          }
> }

I was thinking along the lines of a new object per result.
But that sorta also works, since the handler can be and will be reused.