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Overview
| Comment: | New TIP: 526 |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA3-256: |
0b004d697b9b97127aa6c3918e5c1e47 |
| User & Date: | dkf 2018-11-08 10:16:11 |
Context
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2018-11-10
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| 09:26 | Add precisions in TIP #466 about spaces trimming, -spacemode options, and the fact that no -spacemode value shows text completely identical to the legacy code (slight backwards incompatibility). check-in: 489ef3ca2b user: fvogel tags: trunk | |
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2018-11-08
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| 10:16 | New TIP: 526 check-in: 0b004d697b user: dkf tags: trunk | |
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2018-11-06
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| 15:18 | Corrected vote record check-in: af2513fa1b user: dkf tags: trunk | |
Changes
Changes to index.json.
1 1 {"tip": { 2 + "526":{"url":"./tip/526.md","created":"08-Nov-2018","post-history":"","state":"Draft","tcl-version":"9.0","vote":"Pending","type":"Project","title":"# TIP 526: Make [expr] Only Accept One Argument","author":["Donal K. Fellows <[email protected]>"],"is-jest":false}, 2 3 "525":{"url":"./tip/525.md","keywords":"Tcl, testing, continuous integration","state":"Final","type":"Project","author":["Donal K. Fellows <[email protected]>"],"vote-results":"8/0/0 accepted","votes-for":"KBK, SL, AF, DGP, FV, DKF, AK, JN","votes-against":"none","created":"24-Oct-2018","title":"# TIP 525: Make Tcltest Report Overall Success in a Machine-Readable Way","post-history":"","vote":"Done","tcl-version":"8.5","votes-present":"none","is-jest":false}, 3 4 "524":{"url":"./tip/524.md","keywords":"Tcl, object orientation, customization","state":"Final","vote-summary":"Accepted 2/0/4","type":"Project","author":["Donal K. Fellows <[email protected]>"],"votes-against":"none","votes-for":"DKF, JN","created":"23-Oct-2018","title":"# TIP 524: Custom Definition Dialects for TclOO","post-history":"","vote":"Done","tcl-version":"8.7","tcl-branch":"tip-524","votes-present":"BG, KBK, FV, SL","is-jest":false}, 4 - "523":{"url":"./tip/523.md","keywords":"queue, stack, pop","state":"Final","vote-summary":"Accepted 7/0/0","type":"Project","author":["Peter Spjuth <[email protected]>"],"votes-against":"none","votes-for":"DKF, KBK, JN, DGP, FV, SL","created":"22-Oct-2018","title":"# TIP 523: New lpop command","post-history":"","vote":"Done","tcl-version":"8.7","tcl-branch":"tip-523","votes-present":"BG","is-jest":false}, 5 + "523":{"url":"./tip/523.md","keywords":"queue, stack, pop","state":"Final","vote-summary":"Accepted 7/0/0","type":"Project","author":["Peter Spjuth <[email protected]>"],"votes-against":"none","votes-for":"DKF, BG, KBK, JN, DGP, FV, SL","created":"22-Oct-2018","title":"# TIP 523: New lpop command","post-history":"","vote":"Done","tcl-version":"8.7","tcl-branch":"tip-523","votes-present":"none","is-jest":false}, 5 6 "522":{"url":"./tip/522.md","keywords":"tcltest, error codes","state":"Final","type":"Project","author":["Peter Spjuth <[email protected]>"],"vote-results":"8/0/0 accepted","votes-for":"KBK, SL, AF, DGP, FV, DKF, AK, JN","votes-against":"none","created":"22-Oct-2018","title":"# TIP 522: Test error codes with Tcltest","post-history":"","tcl-branch":"tip-522","vote":"Done","tcl-version":"8.7","votes-present":"none","is-jest":false}, 6 7 "521":{"url":"./tip/521.md","keywords":"Tcl, floating point, NaN, not a number","created":"21 October 2018","post-history":"","state":"Draft","tcl-version":"8.7","vote":"Pending","type":"Project","title":"# TIP 521: Floating Point Classification Functions","author":["Kevin B. Kenny <[email protected]>"],"is-jest":false}, 7 8 "520":{"url":"./tip/520.md","keywords":"Tcl, floating point, NaN, not a number","created":"18 October 2018","post-history":"","state":"Draft","tcl-branch":"tip-520","tcl-version":"8.7","vote":"Pending","type":"Project","title":"# TIP 520: Make NaN Quiet","author":["Kevin B. Kenny <[email protected]>"],"is-jest":false}, 8 9 "519":{"url":"./tip/519.md","":"","keywords":"TclOO","state":"Final","vote-summary":"Accepted 4/0/2","this tip proposes to extend the `method` subcommand of the `oo":":define` command","type":"Project","author":["Pietro Cerutti <[email protected]>"],"votes-against":"none","votes-for":"DKF, KBK, JN, SL","follows":"","oo":":define RPCClient {","created":"18-Oct-2018","title":"# TIP 519: Inline export/unexport option to TclOO method definition","the class definition in the previous example would then be as follows":"","post-history":"","vote":"Done","tcl-version":"8.7","tcl-branch":"tip-519","votes-present":"BG, FV","is-jest":false}, 9 10 "518":{"url":"./tip/518.md","keywords":"Tk","state":"Final","vote-summary":"Accepted 6/0/0","type":"Project","tk-branch":"tip518-event-last-child-unmanaged","author":["Harald Oehlmann <[email protected]>"],"votes-against":"none","votes-for":"DKF, BG, KBK, JN, FV, SL","created":"22-Sep-2018","title":"# TIP 518: Virtual Event when Last Child is not Managed any more","post-history":"","vote":"Done","tcl-version":"8.7","votes-present":"none","is-jest":false}, 10 11 "517":{"url":"./tip/517.md","keywords":"tk menu","created":"13-Sept-2018","post-history":"","state":"Final","tk-branch":"tip-517","tcl-version":"8.7","vote":"Done","type":"Project","title":"# TIP 517: Add -activerelief Configuration Option to the menu widget","author":["Francois Vogel <[email protected]>"],"is-jest":false}, 11 12 "516":{"url":"./tip/516.md","keywords":"Tcl, TclOO","state":"Final","type":"Project","author":["Donal K. Fellows <[email protected]>"],"vote-results":"4/0/5 accepted","votes-for":"DKF, JN, JD, AK","votes-against":"none","created":"7-Sept-2018","title":"# TIP 516: More OO Slot Operations","post-history":"","tcl-branch":"tip-516","vote":"Done","tcl-version":"8.7","votes-present":"BG, KBK, DGP, FV, SL","is-jest":false}, ................................................................................ 522 523 "5":{"url":"./tip/5.md","created":"17-Oct-2000","post-history":"","state":"Final","vote":"Done","tcl-version":"8.4","type":"Project","title":"# TIP 5: Make TkClassProcs and TkSetClassProcs Public and Extensible","author":["Eric Melski <[email protected]>"],"is-jest":false}, 523 524 "4":{"url":"./tip/4.md","created":"26-Oct-2000","post-history":"","state":"Draft","vote":"Pending","type":"Informative","title":"# TIP 4: Tcl Release and Distribution Philosophy","discussions-to":"news:comp.lang.tcl","author":["Brent Welch <[email protected]>","Donal K. Fellows <[email protected]>","Larry W. Virden <[email protected]>","Larry W. Virden <[email protected]>"],"is-jest":false}, 524 525 "3":{"url":"./tip/3.md","created":"14-Sep-2000","post-history":"","state":"Accepted","vote":"Done","type":"Process","title":"# TIP 3: TIP Format","author":["Andreas Kupries <[email protected]>","Donal K. Fellows <[email protected]>"],"is-jest":false}, 525 526 "2":{"url":"./tip/2.md","created":"12-Sep-2000","post-history":"","state":"Draft","vote":"Pending","type":"Process","title":"# TIP 2: TIP Guidelines","author":["Andreas Kupries <[email protected]>","Donal K. Fellows <[email protected]>","Don Porter <[email protected]>","Mo DeJong <[email protected]>","Larry W. Virden <[email protected]>","Kevin Kenny <[email protected]>"],"is-jest":false}, 526 527 "1":{"url":"./tip/1.md","created":"14-Sep-2000","post-history":"","state":"Active","vote":"No voting","type":"Informational","title":"# TIP 1: TIP Index","author":["TIP Editor <[email protected]>"],"is-jest":false}, 527 528 "0":{"url":"./tip/0.md","created":"11-Dec-2000","post-history":"","state":"Final","vote":"Done","type":"Process","title":"# TIP 0: Tcl Core Team Basic Rules","author":["John Ousterhout <[email protected]>"],"is-jest":false}, 528 529 "@min": 0, 529 - "@max": 525 530 -}, "@timestamp": 1541517293} 530 + "@max": 526 531 +}, "@timestamp": 1541672033}
Changes to index.md.
116 116 <th>Type</th> 117 117 <th>Tcl Version</th> 118 118 <th>Status</th> 119 119 <th>Title</th> 120 120 <th>Impl.</th> 121 121 </tr></thead><tbody> 122 122 123 +<tr class='project projectdraft projectdraft90 project90'> 124 +<td valign='top'><a href='./tip/526.md'>526</a></td> 125 +<td valign='top'>Project</td> 126 +<td valign='top'>9.0</td> 127 +<td valign='top'>Draft</td> 128 +<td valign='top'># TIP 526: Make [expr] Only Accept One Argument</td> 129 +<td></td> 130 +</tr> 123 131 <tr class='project projectfinal projectfinal85 project85'> 124 132 <td valign='top'><a href='./tip/525.md'>525</a></td> 125 133 <td valign='top'>Project</td> 126 134 <td valign='top'>8.5</td> 127 135 <td valign='top'>Final</td> 128 136 <td valign='top'># TIP 525: Make Tcltest Report Overall Success in a Machine-Readable Way</td> 129 137 <td></td>
Added tip/526.md.
1 +# TIP 526: Make [expr] Only Accept One Argument 2 + Author: Donal K. Fellows <[email protected]> 3 + State: Draft 4 + Type: Project 5 + Vote: Pending 6 + Created: 08-Nov-2018 7 + Tcl-Version: 9.0 8 + Post-History: 9 +------ 10 + 11 +# Abstract 12 + 13 +This TIP proposes that `expr` should only accept a single argument and stop 14 +accepting and concatenating arguments. 15 + 16 +# Rationale and Discussion 17 + 18 +A very common fault of `expr` usage is to fail to brace expressions. This was 19 +semi-good practice in Tcl 7.6 and before as Tcl's substitution phase was 20 +faster than the expression evaluation engine's, but it was always a little 21 +tricky even then as it depended on you being sure that the substituted values 22 +were numeric for safety. When that critical side condition didn't hold, it 23 +resulted in unsafe code: 24 + 25 + proc addFive {x} { 26 + expr $x + 5 27 + } 28 + puts [addFive 17]; # ==> 22 29 + puts [addFive {[exec format C:]}]; # OOPS! 30 + 31 +From Tcl 8.0 onwards, this was no longer a good idea. The bytecode compiler is 32 +able to generate compiled code ahead of time for braced expressions, but is 33 +not able to do so (usefullly) if any of the arguments to `expr` are unbraced. 34 +Of course, we want to be able to use an unbraced argument occasionally, such 35 +as when we take an expression as an argument from elsewhere, but those are 36 +very much the unusual case: almost always, a call to `expr` with any argument 37 +unbraced is _both_ a performance bug and a security bug. 38 + 39 +Because this is so strongly the case, there are uses of Tcl that are almost 40 +always a problem; for example: 41 + 42 + expr $x >= "inf"; # where $x is expected to be a string 43 + 44 +# Proposal 45 + 46 +To reduce the incidence of this, I propose that in Tcl 9.0 the `expr` command 47 +should only take a single argument. It most definitely isn't a total fix for 48 +this — a total fix isn't really possible without making the `expr` command 49 +special in the Tcl base language, and that goes against the general principle 50 +that _nothing_ is special there — but it will at least reduce the incidence a 51 +bit by encouraging people to either brace their expressions or be very clear 52 +that they are not doing so. 53 + 54 +This will leave virtually all correct code working, and yet force code that 55 +has a problem to acknowledge the fact. 56 + 57 +Supported cases: 58 + 59 + 1. Braced expressions: 60 + 61 + expr {$x * 5} 62 + 63 + 2. Expressions in variables: 64 + 65 + set theExpression {$x * 5} 66 + expr $theExpression 67 + 68 + 3. Expressions from commands: 69 + 70 + expr [dict get $myExpressions thisCase] 71 + 72 +Cases that work because we can't stop them without breaking the language: 73 + 74 + 1. Expressions in double quotes: 75 + 76 + expr "$x * 5" 77 + 78 + 2. Expressions with unquoted compound substitutions: 79 + 80 + expr $x*5+[llength $y] 81 + 82 +Cases that are outright rejected: 83 + 84 + 1. Expressions with multiple arguments: 85 + 86 + expr $x * 5 87 + 88 + 2. Expressions with multiple literal arguments (uncommon): 89 + 90 + expr {$x} *5 91 + 92 +## Workarounds for Broken Old Code 93 + 94 +The cases where someone genuinely needs the old behaviour can be handled by 95 +them using `concat` (or `string cat`, depending on exact requirements) 96 +explicitly to make the expression: 97 + 98 + set x {2 + 3} 99 + expr [concat $x * 5] 100 + 101 +That still has the faults, but now at least looks like it is doing something 102 +tricky. Which it is, given that the actual behaviour of the equivalent code in 103 +Tcl 8 is so messy. Another alternative (and a better one in this particular 104 +case) is: 105 + 106 + set x {2 + 3} 107 + expr {[expr $x] * 5} 108 + 109 +That also looks weird, but is better in that it only has the potential for 110 +trouble in one place and allows for better compilation of the outer parts of 111 +the expression. (Yes, it produces a different result from the other code. This 112 +is likely to be a good thing in almost all cases.)