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PONeed meta-programming magic to define a mother lode of bit fields in an error-free way
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  1. PONeed meta-programming magic to define a mother lode of bit fields in an error-free way
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    copied!<p>The goal is to control which types of users are allowed to perform which operations at the UI level. This code has been in place for a while; I just want to improve it a bit. The file which I am trying to improve should probably be auto-generated, but that would be too big of a change, so I seek a simpler solution.</p> <p>A file which we shall call <code>PermissionBits.h</code> has a bunch of these:</p> <pre><code>// Here names are mangled; for example XYZ_OP_A is: // permission to operation A in category/context XYZ // SCU64 = static const unsigned __int64 // Some namespaces utilize all 64 bits // The actual values (as long as they are proper bit fields) // do not matter - they are always used by name namespace XYZPermissionBits { SCU64 XYZ_OP_A = 1UI64 &lt;&lt; 0; // 1 = 0x0000000000000001 SCU64 XYZ_OP_B = 1UI64 &lt;&lt; 1; // 2 = 0x0000000000000002 SCU64 XYZ_OP_C = 1UI64 &lt;&lt; 2; // 4 = 0x0000000000000004 SCU64 XYZ_OP_C = 1UI64 &lt;&lt; 3; // 8 = 0x0000000000000008 SCU64 XYZ_OP_D = 1UI64 &lt;&lt; 4; // 16 = 0x0000000000000010 SCU64 XYZ_OP_E = 1UI64 &lt;&lt; 5; // 32 = 0x0000000000000020 SCU64 XYZ_OP_F = 1UI64 &lt;&lt; 6; // 64 = 0x0000000000000040 SCU64 XYZ_OP_G = 1UI64 &lt;&lt; 7; // 128 = 0x0000000000000080 SCU64 XYZ_OP_H = 1UI64 &lt;&lt; 8; // 256 = 0x0000000000000100 SCU64 XYZ_OP_I = 1UI64 &lt;&lt; 9; // 512 = 0x0000000000000200 SCU64 XYZ_OP_J = 1UI64 &lt;&lt; 10; // 1024 = 0x0000000000000400 SCU64 XYZ_OP_K = 1UI64 &lt;&lt; 11; // 2048 = 0x0000000000000800 SCU64 XYZ_OP_L = 1UI64 &lt;&lt; 12; // 4096 = 0x0000000000001000 } </code></pre> <p>Even with the help of <code>1UI64 &lt;&lt; &lt;numBits&gt;;</code> shortcut there are still problems, as coders create flags with duplicate values, make typos, etc.</p> <p>Ideally I would like a macro which can be nicely formatted and look like:</p> <pre><code>BITFIELDS_FOR_NAMESPACE( //*************** &lt;&lt;== I want to make the namespace name more vivid XYZPermissionBits, //*************** &lt;&lt;== somehow if that is possible. It is not a must-have. XYZ_OP_A, // Being able to add a comment here would be nice, but not critical XYZ_OP_B, XYZ_OP_C, XYZ_OP_D, XYZ_OP_E, XYZ_OP_F, XYZ_OP_G, XYZ_OP_H, XYZ_OP_I, XYZ_OP_J, XYZ_OP_K, XYZ_OP_L ) </code></pre> <p>I would like this macro be flexible and prevent me from entering less than 2 or more than 65 arguments - namespace name + 64 flags. Is it possible to do what I want or close to it, or should I resort to generated code? What other advice do you have?</p>
 

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