{ "fileName": "Counters.sol", "contractName": "Counters", "source": "// SPDX-License-Identifier: MIT\n\npragma solidity ^0.7.0;\n\nimport \"../math/SafeMath.sol\";\n\n/**\n * @title Counters\n * @author Matt Condon (@shrugs)\n * @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number\n * of elements in a mapping, issuing ERC721 ids, or counting request ids.\n *\n * Include with `using Counters for Counters.Counter;`\n * Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the {SafeMath}\n * overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never\n * directly accessed.\n */\nlibrary Counters {\n using SafeMath for uint256;\n\n struct Counter {\n // This variable should never be directly accessed by users of the library: interactions must be restricted to\n // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add\n // this feature: see https://github.com/ethereum/solidity/issues/4637\n uint256 _value; // default: 0\n }\n\n function current(Counter storage counter) internal view returns (uint256) {\n return counter._value;\n }\n\n function increment(Counter storage counter) internal {\n // The {SafeMath} overflow check can be skipped here, see the comment at the top\n counter._value += 1;\n }\n\n function decrement(Counter storage counter) internal {\n counter._value = counter._value.sub(1);\n }\n}\n", "sourcePath": "contracts/utils/Counters.sol", "sourceMap": "662:848:106:-:0;;;;;;;;;;;;;;;;;;;;;;;;;", "deployedSourceMap": "662:848:106:-:0;;;;;;;;", "abi": [], "ast": { "absolutePath": "contracts/utils/Counters.sol", "exportedSymbols": { "Counters": [ 12946 ] }, "id": 12947, "license": "MIT", "nodeType": "SourceUnit", "nodes": [ { "id": 12898, "literals": [ "solidity", "^", "0.7", ".0" ], "nodeType": "PragmaDirective", "src": "33:23:106" }, { "absolutePath": "contracts/math/SafeMath.sol", "file": "../math/SafeMath.sol", "id": 12899, "nodeType": "ImportDirective", "scope": 12947, "sourceUnit": 2422, "src": "58:30:106", "symbolAliases": [], "unitAlias": "" }, { "abstract": false, "baseContracts": [], "contractDependencies": [], "contractKind": "library", "documentation": { "id": 12900, "nodeType": "StructuredDocumentation", "src": "90:571:106", "text": " @title Counters\n @author Matt Condon (@shrugs)\n @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number\n of elements in a mapping, issuing ERC721 ids, or counting request ids.\n Include with `using Counters for Counters.Counter;`\n Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the {SafeMath}\n overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never\n directly accessed." }, "fullyImplemented": true, "id": 12946, "linearizedBaseContracts": [ 12946 ], "name": "Counters", "nodeType": "ContractDefinition", "nodes": [ { "id": 12903, "libraryName": { "contractScope": null, "id": 12901, "name": "SafeMath", "nodeType": "UserDefinedTypeName", "referencedDeclaration": 2421, "src": "691:8:106", "typeDescriptions": { "typeIdentifier": "t_contract$_SafeMath_$2421", "typeString": "library SafeMath" } }, "nodeType": "UsingForDirective", "src": "685:27:106", "typeName": { "id": 12902, "name": "uint256", "nodeType": "ElementaryTypeName", "src": "704:7:106", "typeDescriptions": { "typeIdentifier": "t_uint256", "typeString": "uint256" } } }, { "canonicalName": "Counters.Counter", "id": 12906, "members": [ { "constant": false, "id": 12905, "mutability": "mutable", "name": "_value", "nodeType": "VariableDeclaration", "overrides": null, "scope": 12906, "src": 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