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<H2>Issue STRING-OUTPUT-STREAM-BASHING Writeup</H2>
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<PRE><B>Issue:</B> <A HREF="iss330.htm">STRING-OUTPUT-STREAM-BASHING</A><P>
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<B>References:</B> <A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>GET-OUTPUT-STREAM-STRING</B></A><P>
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<A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A><P>
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Related issues: <A HREF="iss240.htm">MAPPING-DESTRUCTIVE-INTERACTION</A><P>
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<A HREF="iss364.htm">WITH-OUTPUT-TO-STRING-APPEND-STYLE</A><P>
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<B>Category:</B> CLARIFICATION<P>
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<B>Edit history:</B> V1, 12 Feb 1991, Sandra Loosemore<P>
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<P>
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<B>Problem description:<P>
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</B><P>
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Is it valid to call <A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>GET-OUTPUT-STREAM-STRING</B></A> on a stream bound by<P>
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WITH-OUTPUT-TO-STRING? If so, must the <A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A> still <P>
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return a string containing *all* of the collected output to the <P>
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stream? Or should only output collected since the last call to<P>
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<A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>GET-OUTPUT-STREAM-STRING</B></A> be returned?<P>
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<P>
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The ambiguity exists for both the case where no string argument is<P>
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provided to <A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A> (where the string is returned as its<P>
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value) and where a string with a fill pointer is provided and<P>
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destructively modified. There is also a problem with string output<P>
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streams created by calls to <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> when its stream argument is <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A> or<P>
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a string with a fill pointer, although users have to try harder to<P>
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get their hands on the stream object in that case.<P>
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<P>
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It is also not clear what the effects of destructive modifications to<P>
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a string supplied as an argument to <A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A> or <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A><P>
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are supposed to be.<P>
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<P>
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<B>Proposal (STRING-OUTPUT-STREAM-BASHING:UNDEFINED):<P>
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</B><P>
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Clarify that the consequences of calling <A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>GET-OUTPUT-STREAM-STRING</B></A><P>
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on a stream created by <A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A> or <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> are undefined.<P>
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In the cases where a string argument with a fill pointer is supplied<P>
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as an argument to <A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A> or <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A>, the consequences<P>
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are undefined if destructive modifications are performed directly on<P>
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the string during the dynamic extent of the call.<P>
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<P>
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<B>Examples:<P>
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</B><P>
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#1: (<A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>with-output-to-string</B></A> (s)<P>
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(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#prin1"><B>prin1</B></A> 'foo s) (<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#print"><B>print</B></A> (<A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>get-output-stream-string</B></A> s))<P>
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(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#prin1"><B>prin1</B></A> 'bar s) (<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#print"><B>print</B></A> (<A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>get-output-stream-string</B></A> s)))<P>
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<P>
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=> Under proposal UNDEFINED, this program is in error.<P>
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<P>
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#2: (let ((x (<A REL=DEFINITION HREF="../Body/f_mk_ar.htm#make-array"><B>make-array</B></A> 100 :element-type '<A REL=DEFINITION HREF="../Body/t_std_ch.htm#standard-char"><B>standard-char</B></A> :fill-pointer 0)))<P>
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(<A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>with-output-to-string</B></A> (s x)<P>
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(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#prin1"><B>prin1</B></A> 'foo s) (<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#print"><B>print</B></A> (<A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>get-output-stream-string</B></A> s))<P>
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(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#prin1"><B>prin1</B></A> 'bar s) (<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#print"><B>print</B></A> (<A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>get-output-stream-string</B></A> s)))<P>
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x)<P>
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<P>
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=> Under proposal UNDEFINED, this program is in error.<P>
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<P>
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#3: (let ((x (<A REL=DEFINITION HREF="../Body/f_mk_ar.htm#make-array"><B>make-array</B></A> 100 :element-type '<A REL=DEFINITION HREF="../Body/t_std_ch.htm#standard-char"><B>standard-char</B></A> :fill-pointer 0)))<P>
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(<A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>with-output-to-string</B></A> (s x)<P>
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(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#prin1"><B>prin1</B></A> 'foo s) (<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>setf</B></A> (<A REL=DEFINITION HREF="../Body/f_fill_p.htm#fill-pointer"><B>fill-pointer</B></A> x) 0)<P>
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(<A REL=DEFINITION HREF="../Body/f_wr_pr.htm#prin1"><B>prin1</B></A> 'bar s) (<A REL=DEFINITION HREF="../Body/a_setf.htm#setf"><B>setf</B></A> (<A REL=DEFINITION HREF="../Body/f_fill_p.htm#fill-pointer"><B>fill-pointer</B></A> x) 0))<P>
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x)<P>
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<P>
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=> Under proposal UNDEFINED, this program is in error.<P>
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<P>
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<B>Rationale:<P>
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</B><P>
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Calling <A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>GET-OUTPUT-STREAM-STRING</B></A> is a destructive modification of<P>
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the stream being manipulated by <A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A> or <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A>. <P>
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It would be consistent with issue <A HREF="iss240.htm">MAPPING-DESTRUCTIVE-INTERACTION</A> <P>
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to prohibit this. Likewise, some implementations become confused if<P>
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the string with fill pointer underlying a string output stream is<P>
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modified directly.<P>
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<P>
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<B>Current Practice:<P>
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</B><P>
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Lucid, Allegro, and Symbolics Genera all print "FOO" and "BAR" and <P>
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return "" from test case 1, but vary in the behavior of the other<P>
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cases.<P>
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<P>
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<B>Cost to Implementors:<P>
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</B><P>
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No implementation would be forced to change by this proposal.<P>
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<P>
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<B>Cost to Users:<P>
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</B><P>
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Probably few user programs rely on any particular behavior here.<P>
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<P>
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<B>Cost of non-adoption:<P>
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</B><P>
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Continuing vagueness in the language specification.<P>
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<P>
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<B>Performance impact:<P>
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</B><P>
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N/A<P>
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<P>
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<B>Benefits:<P>
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</B><P>
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The costs of non-adoption are avoided.<P>
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<P>
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<B>Esthetics:<P>
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</B><P>
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It might be more esthetic to try to specify the behavior. In the<P>
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case of <A REL=DEFINITION HREF="../Body/m_w_out_.htm#with-output-to-string"><B>WITH-OUTPUT-TO-STRING</B></A> where no string argument is provided<P>
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and <A REL=DEFINITION HREF="../Body/f_format.htm#format"><B>FORMAT</B></A> with a stream argument of <A REL=DEFINITION HREF="../Body/a_nil.htm#nil"><B>NIL</B></A>, the behavior could easily<P>
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be explained in terms of the obvious implementation of these constructs <P>
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using <A REL=DEFINITION HREF="../Body/f_mk_s_2.htm#make-string-output-stream"><B>MAKE-STRING-OUTPUT-STREAM</B></A> and <A REL=DEFINITION HREF="../Body/f_get_ou.htm#get-output-stream-string"><B>GET-OUTPUT-STREAM-STRING</B></A>. However,<P>
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there are no corresponding primitives for creating a string stream from<P>
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a string with a fill pointer.<P>
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<P>
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<B>Discussion:<P>
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</B><P>
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-------<P>
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</PRE>
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